I would start with adjusting the brakes. Lift one tire off of the ground and give it a spin. You should hear the brake shoes rubbing the brake drum, if you don't, tighten them up until you do. Do all four corners and then take it for a test drive. You should stop in a straight line without having to grabb the steering wheel with a death grip. If it does pull tighten the other side don't loosen the side that is pulling. Also check the brake fluid level.