Keep your workout machines and dumbbells in order. Use the smaller weights first and work your way up to the larger weight like barbells and bench presses, and then eventually work your way up to a machine. The smaller weights uses more of your muscle and you get fatigued easier.
Try to cut down the amount you rest during your time in the gym. Many people have limited time, and you should try and rest less during the beginning of your workout when your muscles are less tired, and at the end you can rest more when they are fatigued.