If you have little or no experience of pvp then 5 boxing might ease it slightly but you are going to suck.

My first battlegrounds I was physically shaking from the adrenalin rush, and was unable to think what to do in battle. I just tried to get my dots up and hoped they died before they got to me (they rarely did). Over time I learnt to be more mobile. Use different approaches and was able to react in battle.

I've not five boxed in BG's but I've BG'ed on three different 70's suggest the following

Here's some general advice.

Get as much pre season 1 gear that can be bought from the quartermasters once you have rep with various factions.

Resilience will help a lot.

I would also suggest taking one of your characters and pvp'ing that one for a bit. If you dont know how to pvp one char properly you won't maximise the 5.

AV is a great place to learn. My first suggestion is to run with the crowd, so you know the layout and objectives inside out.

BG's are about never being in a fair fight. There might be any number of occasions where you would win 1 vs 1 but a second character will join the fray and you've got a graveyard run. Try to ensure that you are the one with backup. ( once you are competent at pvp on one char your multiboxing will ensure you are never in a fair fight in a good way)

Know the abilities of other players.... know their weaknesses. e.g Go to google type wowwiki <yourclass> how to kill a

Know all your own abilities and use them.

For example in pve I rarely used purge on my shaman. In pvp if I see mages with ice shield up (or whatever it is called) I love sending off a lightning bolt and immediately after it's on it's way I purge. Their shield goes down and they take the full damage.

Organise your setup. Look for abilities that are instant or close to it, as well as big damagers that are on a reasonable cooldown. Have them keybound and have the mappings imprinted in your muscle memory so you can trigger an ability without thinking about it.

Over time you will pick up on which abilities you use in battle most. You will also develop an approach to battle against various characters, even different specs of character. (Including learning to run away from fights that you just wont win).

After a decent grounding in single character pvp you will be awesome as a five man.