You just have to stay mobile. I wear Bones of Eao with max agility Bladedancer to move around the map quickly and efficiently. That's the only way to prevent snipers from killing you. The only times I've been killed by snipers were when I was standing still. Imagine each map is like a race track, keep rotating around the entire map and pick off any enemies you see. It can lead to some easy kills and it makes you even harder to kill. Also, choose your engagements wisely. If you're being shot at and you know you're going to lose the gunfight, duck into cover and don't be afraid to run away. After all, that is 1 less death for you, and 100 points less for the enemy team.