Copy your entire game folder to a safe location before changing anything.

Start with a fresh, unmodded copy of the game.

If you have acquired the original, classic version of the game and want to make it playable and stable on modern systems (or ready for mods), follow this standard setup sequence:

Watch this highly rated breakdown for a detailed step-by-step walkthrough on properly setting up and modding San Andreas:

This is the primary library needed to execute custom scripts and mods.