Make sure your computer meets the minimum system requirements stated on the back of the case and that you have the latest drivers for your graphics card.
It's basically down to your hardware, so if it is lacking in processor speed, memory, or video performance, then technically there's nothing that can be done except to upgrade.
If your computer meets the requirements but is still having trouble, then you may need to temporarily disable any firewalls, virus checkers, or other intensive programs running in the background, as these can considerably slow down your games.
Lonesome George
the last of his kind