1. Lower your in game settings.
2. Make sure your screen resolution matches your game resolution.
3. Disable unneeded features such as Aero effects.
4. Disable unneeded programs. Just use Game Booster if you're not sure what to do.
The same thing used to happen to me when I played WoW on a PoS computer. That stuff should help. A little. If not...
5. Upgrade your PC.