Arcade is a real crapshoot, but you can still count on the enemy being just as stupid as your own team (most of the time, anyway).
When I start, I turn 30-45 degrees to one side or another and start climbing with WEP on, I pitch up until my speed is stable at about 150mph. This means I am well above the opening furball, and am in a position to hunt high level bombers. At this stage I am also on the lookout for high value targets, which is mostly any bastard that brought a one-shot trollcannon to the match. KI45s and P39s are always the first things I kill when I can help it, A20s and Beaufighters are also high on my list. If I see one of my HVTs I fly more or less direcly over him, then roll 180 and lay on the elevators. If my target is fast like an A20, this means I'm moving quickly enough to actually keep up with him and do some damage. If my target is something else it means I will probably be approaching from above and just behind him and he won't have a clue I'm coming. I take careful aim, open up at about 1400ft, keep the guns on him until I'm about to ram, then keep diving behind his tail, and pull up without turning. I use my speed and WEP to quickly climb to 3-5k feet while taking stock of my new surroundings, then normally turn around and do it again. Normally my first target is dead, but sometimes they're just crippled. In any case they can't do anything to me because I'm out of guns range by the time they know where I am.
Starting about 5 minutes into the match you can tell who has a clue just by the scoreboards. Look at the top 3-5 names on your side and try to stick with them; look at the top 3-5 names on their side and ambush them whenever possible. Scoreboard hotkey is N, overall map hotkey is M, both are vital to situational awareness. Another handy hotkey is U, which tracks the last bomb/torp you dropped, it is very handy for adjusting your aim against moving targets. And don't forget your number pad, or someone like me will latch onto your ass and you won't have a clue until things start going black.