The AWP is a weapon that decides the match. You want to use everything about the AWP to your advantage, whenever possible. For example, it's price tag. If you know you have no chance of winning the round, but a dead teammate's AWP is nearby, you can pick that up and run away, and give it to your teammate the next round. By doing this you have saved money in that A, you didn't die, giving up $1000 of armor, a $2500 or $3100 gun, plus grenades and possibly a purchased sidearm. And B, the AWP costs $4750. If you can give your teammate the AWP, he can buy you a rifle, and you just saved 2 or 3k. Another example is the fact that because of your double zoom, you can pick up on key details that your teammates may not. Ie, if you double scope and the enemy is pistol rushing somewhere (let's say long A on dust2), and your teammates are on A platform, pretty far away, they can just see the enemy with pistols. If you come up from CT spawn and double zoom, you can see if there are weapons on the enemies backs, indicating a surprise buy. (A good place to see this for yourself is to load up an AWP map, set bots to knives, then look at their back across the map with each level of zoom.)
Some good positions as T to make the crucial shot that makes the oppositions B side weak (unless they rotate a player there, and open themselves at A).
This sorta shots take some practice, so go on a public server, and practice picking off people a split second after they cross the gap.
Picking as a T
This is in my opinion, the easier side of Dust2 to awp from. These are some basic positions to pick a CT awper from.
This is probably the easiest pick to make. A decent CT awper will probably prefire that spot, so you might wanna watch out.
Picking as CT
Picking as CT is a tad bit harder, as the T's are higher than you, have a clearer shot (you have the double doors in front of you, but those are spam able so if the luck factor is high enough, you might bang one trough the doors), and almost always have the time advantage. If your team is overall a little bit worse than the other team, you'd be better off not trying to pick middle, and just watching short a.
The 3 basic picking positions are really commonly used.
The first 2 are risky, but again, a required risk to take. The 3rd is a brilliant position to pick off any T's pushing catwalk (aka short A).