Biceps are a pretty small muscle group, and are at least partially used in a lot of compound and accessory lifts already. It's definitely easy to overwork them if you're paying careful attention or working a program. For actual dedicated curls, I personally try to use a reasonable weight that I can easily control through slow full movements, and that bring me to failure in about the 10 rep range. Three to five sets should be more than enough, when you factor in all the lifts that will hit your biceps throughout the week, such as rows, lat pull downs, etc etc.