From what I gather, Tuesday and Thurs are the best time. Shifty seems to bring a gang in around 8pm EST.
Other than that, if you see 1 or 2 guys in there, hop on in and see what's up. Once a few people log in, and inertia builds up and you can possibly have some nice 4 v4 or more fights.
Alot, or most, of the AvA 'regulars' seem to be much better than average, measured against your typical MA player. My opinion only.
Your AvA score doesn't count against or for your MA score, so if you're worried about your score, you can fly all out in the AvA and still be a score hound in MA.
Generally people don't HO or vulch or gang too much in AvA, but then again, it's always best to keep out of the pipper of the enemy and not have to worry about getting HO'd. It does happen, happened to me tonight in a night of really good players. Still not sure why, it was 1v1 at about 11k. No real good reason to HO on the merge. My fault for getting in front though.
Guess that's about all I can offer. I really like AvA, but I get killed alot in there.