To start out I would do 3 sets of 10 reps. More reps is for building muscle endurance. Lower reps are for strength and power. Don't always do the same amount of reps and sets. You need to mix things up or your muscles will get used to what your doing and wont grow as much. I try sticking to higher reps for compound lifts like deadlifts and squats, and do medium to higher reps with isolation exercises like bicep curls or tricep push downs. Low reps would be between 1-6. high reps would be anything above 10.