Different games have different system requirements. For a game to run smoothly you will need to exceed the minimum requirements regarding the (CPU, graphics card, memory, storage space, etc). The easiest way to do this is to buy newer and powerful components for your computer.
For games to run smoothly I recommend an Intel i5/AMD equivalent processor with a graphic card having 2 GB GDDR3/5 memory running at ~2 GHz on a 256 bit stream and dual/triple channel 6 GB DDR3 @ 1333 MHz.
This example configuration is more than enough to play the latest games smoothly.