A good practice is to use 10x zoom for extreme range shots ONLY, unless you're in a position you can stay still for a moment. Because 10x zoom is slower movement, so if your target sprints you will lose them (unless it's extreme range). 5x zoom works well for mid- to long-range but not very well for extreme range and it is fast enough to keep up with fleeing foes.
Quick-scoping works well for some people. The hardest part is knowing when to use a quick-scope over regular scoping. The idea is to get a player in your sights to where you could no-scope them, but go to 5x zoom just before you shoot. This increases accuracy, but can be tricky to pull off at times.
Camping with a sniper is never a good idea, as that player will be top on the other teams hit list, but pausing for a kill can be good.
If you see a sniper aiming at you, strafe away. Do not stop moving until there's something solid between you and them. If you don't think you can escape and/or you're in a position to return fire, strafe randomly and start shooting.
During reload (when the magazine is in the gun, but the weapon is still raised, press the switch weapon button twice quickly. This will shave a small amount off of your reload time.
No-scoping when your moving is actually easier than no-scoping when your standing still because you can sidestep and shoot simultaneously. Doing this properly means you hit them, but they miss you. Your strafe matters for this, so keep practicing it, and don't be afraid to quick-scope in close. You need to be careful, but assuming they aren't too close this can often give you a little extra edge in the fight.
