GTA San Andreas Guide

Do not spend all your cash on guns before the desert unlocks, You'll understand why when you get there.
Try to swim underwater a bit during the first 2 zones so you don't get blocked out of a mission halfway the game and have to grind; it is the only mission requiring you to make a character stat higher.
Bikes start out decent but if you get the handling skill maxxed out they are almost impossible to fall off.
The flightschool isn't remotely as bad as people make it out to be unless you want to 100% it.
If you're playing on the PC, it'd be a good idea to have a controller for flying planes.
Don't bother taking over gang territory at the beginning of the game.