Find city maps with good choke points (such as Karkand...). Be a medic - itll be helpful because you're going to want to heal yourself. Don't worry about ammo - chances are you will die before you ever run out of your 7 pistol clips, and if you DO run out of ammo, just pick up the last person you killeds kit. Get to know the spawn points - i.e., where people spawn when they spawn at different flags. My best tip is to think about which flags people are most likely to spawn at (like Hotel at Karkand for the first flag), and lay down somewhere near the spawn point for someone, but BEHIND the way that they would be facing when they spawn. If it sounds confusing it's really not - when you spawn you always spawn facing the same way, so make sure you're behind that person when they spawn. After they do, pop off a quick few rounds - aim for the chest as well. Your pistol will always move itself up a littl ebit when you shoot, so chances are ifyou fire off 3-5 rounds, one might hit them in the head and finish them off for you.
Hope I could help