To easily level up the strength and shooting skill stats to 100 in approximately ten minutes, use the following trick. First, buy a lot of pistol ammunition, and then find a bus. Jump on top of the bus, and stomp on it while it is moving. Make sure to move back and forth or you will fall off after stomping. Once your strength is at 100, shoot the middle of the bus until your shooting skill is at 100. The bus should be able to take all the bullets without being destroyed.