My goals are two-fold:
1) Support the team. I'm almost always in a Raven Prime or APC in the first wave because these are force multipliers that help the rest of my team be more effective. I will also take the Osiris A (iirc) for its ERLBL anti-BA capabilities, or any ECM/GECM medium to hunt down LTs. Recently I've been enjoying the RAC5 Hollander II and the "Warthog" Bushwacker; I've killed quite a few Aeros and VTOLs but more than anything the ability to sit on a hilltop and effectively engage any BA I see is satisfying *and* supportive. More than anything, keeping an eye on the battlefield situation and adjusting to changing requirements - taking an ECM medium to assassinate hidden 'boaters, taking AAA if the team is getting anally probed by UFOs - let me feel like I'm contributing.
2) Kill the enemy. Since we're basically playing team deathmatch I try to take out as many enemies as I can, which means I'll use "cheap" tactics like sniping, NARCing, prioritizing BAs and armor, LTing, missile pop-tarting, flanking under ECM, and staying close to the base... *as* *necessary*. I'll pop a light with an HGauss, hell yeah I will, and I'll flee a dying mech and fight on on foot for as long as possible, so long as it looks like I can take out another enemy. Since I don't focus on survival to the exclusion of all else sometimes my D/K ratio is low, but I almost always end up in the top 3~5 on my team.
I like to feel like I'm providing support to my team so I try to communicate as much as possible; being an ex-tanker the ideas of combined-arms fighting and coordination are sort of second nature now. On the flip side, I don't play like it's a sim: there's not enough customization yet to really feel like I'm playing a personalized character and so far there aren't any game modes that reward survival.
In reply to the guy who complained about BAs being useless, well, I'm sorry you feel that way. I used to curse BAs, up until I learned how to effectively combat them, but in my experience they have been and continue to be an effective part of the team. They're not going to be downing heavies on their own, for the most part, but they are superb harrassment units that can, in the right hands, destroy snipers, provide TAGging, suppress other BAs, distract parts of a charging unit, and act as forward observers... all useful roles. Anything that can divide the enemy's attention or take the pressure off your own team's expensive assets is useful. Maybe you won't rack up the highest score, but piloting a BA can be very rewarding in its own right.