Dont run out like a fanny, be defencive, that doesnt mean sit in a corner and wait for people to come past, pick a quater of the map, and defend it, try find a gun which matches your playing style, if you like to rush them use ninja pro and an smg, if you like to defend flags/bombs from miles away a sniper obviously, if you like to play defencivly use an assaut e.g scar, tar, acr, m16, m4, always take cover after you have taken a shot, dont stand out in the open, once youve killed someone MOVE, they WILL come back for payback, if your rubbish at getting high streaks use uav, carepackage and pred. Uav helps you and your team out 100%, espesh when rushing.
if you have xbox and want some more help, add me I SHIXX I, Im not exactly amazing, but i 95% of the time go possotive in my matches, with like 23 - 1 or 45 - 10, scores like that, highest streak is 31 and winning streak 33.
make sure you learn most common routes in maps aswell, go into a private match and play with a few mates till you know the maps 100%, you need to know all the camping spots, make your own routes and learn other common routes, will help alot ingame.
hope this helps abit, but these are pretty much the things what got me to an okay standard at this game.