Unless your raid has been "balls on point" for a few weeks (ie: no screw ups, no super excess damage taken, no player deaths) on any particular boss encounter, odds are good that you will have to take the time and explain the fight. Don't succumb to the urge to skip the explanation in favor of 'hurrying up', especially when you don't have alot of experience in that particular encounter. A proper, full explanation can be very valuable in many ways: 1) as a refresher to everybody, including you... 2) accountability : If you explained it to them, and they screw it up, it's their fault. If you did't explain it you'll get all the same excuses: "I forgot" "I didn't know" "I thought that was the other boss". So explain the fights and you will be well rewarded.
So now that we've determined that we have to explain the fight, let's talk about how we explain it. The way you deliver the information is very important to you and your raiders. Try to deliver it in the same format all the time, it'll make it easier for those listening to absorb all the info they need, and it'll keep you from rambling on and repeating yourself, and keep you sounding like you know what you're talking about. It doesn't matter what format you choose, really, just use rule KISS (keep it simple, stupid), don't go off on tangents explaining class specific things, let people decide how to play their own class (ie: don't bet telling the priest where to put his lightwell, he should know / be able to figure out where, once he sees the fight). A few exceptions to this would be telling the paladin he can bubble out, or telling non-healing druids to use tranquility, etc.. So here is an example format for a fight explanation.
This is "name of boss"
A:) This is a "type" type encounter
1:) what ^ means. (ie: council type - bosses share health pool, phase type - "this is a X phase encounter"
2:) how is the fight going to flow (ie: when they get to 50 energy, switch targets, when they get to 0, they go inactive)
B:) Boss Abilities (for council encounters talk about common abilities, like shields on Omnotron)
1:) individual bosses (council type), individual phases (phase type)
a:) abilities
1:) name of ability
2:) what the boss does, visual/audio cues (ie: he starts spraying slime, then adds pop out, or "mix and stir, apply heat" is red vial phase)
3:) how we deal with it
b:) what people need to watch for (ie: poison clouds, adds, or previously noted common mistakes)
c:) specific assignments (interrupts, staggered group heals, stack on player, collapse point, etc.)
So just as an general outline, you can deliver your infomation in a format people can understand and get used to hearing, so they can absorb the information they need to and don't get alot of extra/confusing junk along with it. It's important to be as brief as you can afford to, while still being complete in your explanations, for pacing reasons.
After a wipe, two steps are needed, 1:) figure out what happened. Ask people if you don't know, no shame in sayin "what happened during that red phase? were people not stacked up or what?" and 2:) talk about the problems, "you gotta run away from those slimes, don't just keep dps'ing" or "if you don't stack up you'll get oneshotted, so it's very important". This way you don't just keep bashing your head while people keep making the same mistakes, see a problem; fix a problem. Take note of these mistakes for use in next week's explanation (see B; 1; b above).
In conclusion: Don't underestimate the value of a good, solid fight explanation. If nothing else, it refreshes everyone to the names of the abilities/spells cast, and puts you (as the raid leader) in a position to hold people accountable for their mistakes (which is important, because if you know it's their fault, odds are they know it's their fault too, and they are much more likely to improve next time).
