Rest about 30 sec and do a few more-- even just 2 at maximum
weight. Rest than do even just one more. By now (if you are using enough
weight) your muscle should be screaming. Eat protein within 1/2 hour of lifting. Drink a lot of water to flush the lactic acid out of the muscle. Then rest the next day, or work a different muscle group. Always let the muscles worked have a day to recover, or you'll just breakdown what you build up.