Never go by a percent of your 1RM, that will assume fiber-type ratios which you may not have. (I know they're always WAY off for me).
Choose a weight that you can do 1 and a half reps with. Perform 1 rep, take a 10-20second break, rinse and repeat. Make sure to use a spotter or safety restraints when necessary (i.e. bench press, squats, etc.)