go into a server running kark, try and get on the usmc team, spawn at the top-right most uncap, be a sniper of course, go on top of the hill, and snipe from there. theres a lot of people who are dumb and just run across the map right where you could snipe them... its how i got good at sniping out running targets. and remember, dont lead by too much.
i remember the first time i played as a sniper on bf2. i had just played a game of halo on pc (which im always a sniper on)... i was so used to leading by a ridiculously unrealistic amount, that i got pissed off. then my friend slapped me on the head and called me an idiot.