First off... if you want to play a blaster or blapper, forget defense. There ain't no such beast. Instead, you rely on two things: Active Defense (aka, kill them before they can kill you), and Damage Mitigation (aka, keep them from being able to hit you in the first place).
A.D. is pretty self-explanatory, but I'll lay out the basics before moving on. Nuke, nuke, nuke. Cannot emphasize that enough. For solo play, your nuke will be what you open every fight with and, if you're tuned right, what you finish every fight with. Your nuke will change as you progress. At early levels, it'll be the first AoE or Cone attack you have -- Energy has Torrent (I think?), Archery has Fistful of Arrows, Fire has Fireball, and so on. When you get better, more powerful AoE's, you start pumping them as your nuke instead. And so on. Your nuke, whatever it is, should take every white-con minion it hits into the red if not killing them outright. (Ignoring special cases where they're resistant to your damage type, obviously)
Now that that's out of the way, the tricky bit. Damage Mitigation.
Unlike other archetypes, Blasters don't have crap for defense or resist in any form. The only thing they get is the ability to keep shooting even while mezzed, which is a pretty damn good ability, and is the primary reason you should always take your lowest-tier attacks and pump them up, because when the Carnies mez you, you'll be able to return fire and you want to make it count.
Regardless, every blaster *secondary* gets some nice crowd-control abilities, and you need to learn them, love them, and use them. What you're looking for are stuns, knockbacks, and knockdowns. Holds are great but you won't find many, and Immobs are decent but most enemies have ranged attacks and thus will still be able to hurt you. Don't skip them, but you'll be concentrating on the first three. These need to be slotted for accuracy, to make sure they hit, and for recharge, so you can reapply them constantly. Set bonuses are great once you get into levels to make use of them. If you go the blapper route, you'll be concentrating mostly on your secondary anyway, so there's no excuse not to take them all. Pure blasters can avoid most of them to free up slots for other powers.
Now the trick is to get into the nuke-and-stun mindset. You should open with the attack that will outright kill as many opponents as possible, then while your nuke starts recharging, move to stunning them with your secondaries. On a team, a blaster/blapper should hold fire until the tank/brute/tough scrapper has gained aggro OR the controller/dominator/defender has mezzed them all (note: sleep is not mezzing, in this regard, as your attacks will wake them up and they'll be pissed at you). This is part of Damage Mitigation: if they're not pissed at you, they won't hurt you (and you can kill them). You are not the front-line fighter, even as a blapper: you are artillery... or a hand grenade, in the case of blappers.
Blasters and blappers alike need to think tactically. Take advantage of terrain! If you hit a mob, then immob several of them, step around the nearest corner and let their non-stuck buddies come play. It gives you time to deal with the smaller group first before the others come to mess up your face. This too is part of Damage Mitigation: if they can't see you, they can't hit you.
Finally: concentrate on the high-priority targets. The boss or lieutenant that the tank is pounding on is NOT the high-priority target. They are, in rough order: healers, mezzers, and minions. That's right, minions are higher priority than the Big Nasty. If you're solo, then you can spend a few seconds to stun or immob him; if you haven't done it before your health is down to 75% then it's time to turn it into a running battle or retreat entirely. Once he's stunned, kill off his minions because while they don't do as much damage, there are more of them and they'll mess you up right quick. On a team, you remembered to let the tank grab aggro first, right? So that means the Big Nasty is busy, you can do cleanup around the edges.
Okay, on to specifics. An Energy/Energy Blapper can be amazing in a fight, though I'll note that on teams you're likely to irritate your allies because almost all your powers do knockback. Learn to aim your opponents into corners (take advantage of terrain) so that you don't force the melee fighters to run all over the place to take down their foes.
Your first nuke should be Energy Torrent, which you can get at level 2. It's got decent though not stellar damage, but it also does knockback, meaning you've got a two-for-one special here. For your solo build, slot this bad boy for knockback and unload it at point-blank range. Your enemies will have to spend the time to run back into melee range (which most low-level enemies have to do, unless they just throw Rocks), by which point you should be just about ready to unleash it again.
For secondary powers, you'll learn to adore Power Thrust (it's Torrent, but single target) and Energy Punch (your first disorient, aww). Build Up will fast become your bread-and-butter power, and you'll use it the whole game to make your nuke more nuke-like. With Energy Manip as your secondary, you'll need to get used to switching targets rapidly, since you don't have any good AoE mezzes of any sort -- but you have a lot of Disorients (4!) that you can use -- and if you pop Power Boost beforehand, you can stunlock some targets.
Nuke-and-stun, nuke-and-stun. That's the Blaster/Blapper motto. Because you don't, can't, and won't ever have significant defense or resist. Sure, you can take Tough and Weave, but your base numbers are so low you'll weep in despair when you see what they get you. Hover and Acrobatics help with getting held or mezzed, but as a Blaster you will still be able to attack while mezzed anyway, so what's the point?
--sofaspud
--"Listening to your kid is the audio equivalent of a Salvador Dali painting, Spud." --OpMegs
A.D. is pretty self-explanatory, but I'll lay out the basics before moving on. Nuke, nuke, nuke. Cannot emphasize that enough. For solo play, your nuke will be what you open every fight with and, if you're tuned right, what you finish every fight with. Your nuke will change as you progress. At early levels, it'll be the first AoE or Cone attack you have -- Energy has Torrent (I think?), Archery has Fistful of Arrows, Fire has Fireball, and so on. When you get better, more powerful AoE's, you start pumping them as your nuke instead. And so on. Your nuke, whatever it is, should take every white-con minion it hits into the red if not killing them outright. (Ignoring special cases where they're resistant to your damage type, obviously)
Now that that's out of the way, the tricky bit. Damage Mitigation.
Unlike other archetypes, Blasters don't have crap for defense or resist in any form. The only thing they get is the ability to keep shooting even while mezzed, which is a pretty damn good ability, and is the primary reason you should always take your lowest-tier attacks and pump them up, because when the Carnies mez you, you'll be able to return fire and you want to make it count.
Regardless, every blaster *secondary* gets some nice crowd-control abilities, and you need to learn them, love them, and use them. What you're looking for are stuns, knockbacks, and knockdowns. Holds are great but you won't find many, and Immobs are decent but most enemies have ranged attacks and thus will still be able to hurt you. Don't skip them, but you'll be concentrating on the first three. These need to be slotted for accuracy, to make sure they hit, and for recharge, so you can reapply them constantly. Set bonuses are great once you get into levels to make use of them. If you go the blapper route, you'll be concentrating mostly on your secondary anyway, so there's no excuse not to take them all. Pure blasters can avoid most of them to free up slots for other powers.
Now the trick is to get into the nuke-and-stun mindset. You should open with the attack that will outright kill as many opponents as possible, then while your nuke starts recharging, move to stunning them with your secondaries. On a team, a blaster/blapper should hold fire until the tank/brute/tough scrapper has gained aggro OR the controller/dominator/defender has mezzed them all (note: sleep is not mezzing, in this regard, as your attacks will wake them up and they'll be pissed at you). This is part of Damage Mitigation: if they're not pissed at you, they won't hurt you (and you can kill them). You are not the front-line fighter, even as a blapper: you are artillery... or a hand grenade, in the case of blappers.
Blasters and blappers alike need to think tactically. Take advantage of terrain! If you hit a mob, then immob several of them, step around the nearest corner and let their non-stuck buddies come play. It gives you time to deal with the smaller group first before the others come to mess up your face. This too is part of Damage Mitigation: if they can't see you, they can't hit you.
Finally: concentrate on the high-priority targets. The boss or lieutenant that the tank is pounding on is NOT the high-priority target. They are, in rough order: healers, mezzers, and minions. That's right, minions are higher priority than the Big Nasty. If you're solo, then you can spend a few seconds to stun or immob him; if you haven't done it before your health is down to 75% then it's time to turn it into a running battle or retreat entirely. Once he's stunned, kill off his minions because while they don't do as much damage, there are more of them and they'll mess you up right quick. On a team, you remembered to let the tank grab aggro first, right? So that means the Big Nasty is busy, you can do cleanup around the edges.
Okay, on to specifics. An Energy/Energy Blapper can be amazing in a fight, though I'll note that on teams you're likely to irritate your allies because almost all your powers do knockback. Learn to aim your opponents into corners (take advantage of terrain) so that you don't force the melee fighters to run all over the place to take down their foes.
Your first nuke should be Energy Torrent, which you can get at level 2. It's got decent though not stellar damage, but it also does knockback, meaning you've got a two-for-one special here. For your solo build, slot this bad boy for knockback and unload it at point-blank range. Your enemies will have to spend the time to run back into melee range (which most low-level enemies have to do, unless they just throw Rocks), by which point you should be just about ready to unleash it again.
For secondary powers, you'll learn to adore Power Thrust (it's Torrent, but single target) and Energy Punch (your first disorient, aww). Build Up will fast become your bread-and-butter power, and you'll use it the whole game to make your nuke more nuke-like. With Energy Manip as your secondary, you'll need to get used to switching targets rapidly, since you don't have any good AoE mezzes of any sort -- but you have a lot of Disorients (4!) that you can use -- and if you pop Power Boost beforehand, you can stunlock some targets.
Nuke-and-stun, nuke-and-stun. That's the Blaster/Blapper motto. Because you don't, can't, and won't ever have significant defense or resist. Sure, you can take Tough and Weave, but your base numbers are so low you'll weep in despair when you see what they get you. Hover and Acrobatics help with getting held or mezzed, but as a Blaster you will still be able to attack while mezzed anyway, so what's the point?
--sofaspud
--"Listening to your kid is the audio equivalent of a Salvador Dali painting, Spud." --OpMegs