Haha. Well it took me a while to actually grasp sniping. But now its all i do. The one most important thing, but you probably don't want to hear, is that you need lots of practice.
Okay first of all, you should start out with a good sniper. Depending on you style, and what games you play, picking the right sniper can be difficult.
If you're like me, and like close combat type sniping, then most definitely get a dsr. It is great for games like Sniper no Semi but it is a horrible defense against long range sniping. So don't get a dsr if you are planning on sniping in things like Escort.
TPG is a very good sniper when it comes to long range. It is very slow if you don't know how to qs(quick scope). But the damage makes up for that. It has 110 damage so its pretty good. If you get really good with it, no one will be able to stop you.
FR-F2 is kinda in between. It is great at short range and long range. It is the best sniper you should start out with if you are just beginning to learn to snipe.
In the beginning, you should start out sniping in the sniping gallery. It is great practice and will get your accuracy up.
If you can't snipe, don't do demolitions, it will only bring your s/d down.
Escort is great for practicing your long distance sniping. TPG is best for doing something like escort.
Well I don't have many tricks for sniping but I can tell you this:
First, the DragScope. Its when you slide the mouse to hit your target. It involves very good reactions on your part and probably the best trick you can learn as a sniper.
Second is the qs or quick scope. Many people quick scope with 3-1. That is very hard for me and i personally dont do it. Only pros know how to do it that way. This is my way around it. Use your mouse wheel. You will get used to it way faster then 3-1. Up-Down on the mouse wheel is the way I do it but you can do it Down-Up. You can also use "QQ". Many people seem to like that one over the mouse wheel and 3-1. I think it's difficult to use considering you probably want to be moving while you qs. Same thing goes for 3-1.
That's all I have for you. Hopefully you will get better at sniping over time and become a pro. Hope to see you in-game!