Visit your public library or a local bookstore for a book on positive discipline. Sit down with your son when you are both calm and explain your expectations for his behavior. Let him help you determine rules, rewards, and consequences to help him improve his behavior at home. Pick one or two behaviors on which to work at first; as those improve, move on to others.
Keep in mind that rewards do not have to cost money. Reading an extra bedtime story or taking a walk around the block just with you can be terrific rewards for an eight-year-old. Determine a bigger reward (having friends over to play on the weekend or going camping) that your son can earn for having no problems for three days in a week.
The key to any system like this is consistency over a long period of time. You will need to plan to stick with the reward-and-consequence system for weeks; don't stop using it when you begin to see improvement.