I've been playing this game everyday for... the past month or so. Here are a few things I've learned:
1. If you're spending real money on this, splurge and buy a Lowe. It's a German heavy. Best sniping gun in the game, but slow as heck. Makes a #%&*$#-load of credits though. I remember looking at upgrades costing 500,000 creds and thinking "how could anyone afford that?" My Lowe makes me 20-30K in profits on a good battle (and I'm not playing with a premium account so I don't get the 50% bonus XP and credits), so 500,000 is just a couple of easy fights away.
2. Playing with a platoon or a clan increases the fun factor a lot. Sure, you may still be doomed by the matchmaker but it's fun doing battles and coordinating with other players, not mindlessly flailing about the battlefield.
3. Know your role. You may be in a heavy tank but that heavy might be better suited to sniping than being a front-line tank.
4. Look at the other guys. Sometimes you may luck on a game wherein other players know what they are doing, leap-frog advancing towards the enemy. Go and give them support.
5. Have fun. You will not always win, you will not always be alive at the end of the battle. Make your presence count and make your contribution to the team.