I'm a decent to below average sniper, from time to time I'll go on a tear and it seems like every shot is a head-shot but otherwise I'm better in other roles. I know a couple good snipers and what they say is its all about predicting movements for which most people have a pattern they can exploit. One of my friends put it this way, even the best players when they're dodging left and right have a pattern, often something as simple as going right more often then left this means if you know the dodge distance you can shoot for a right dodge and you'll nail them more often then not. Also most maps have common sniper locations so the best option is not to use a common location because players will often let down their guard.