Instead of doing the same amount of reps for every set try pyramiding your reps. Pyramiding allows you to work throughout a whole range of rep ranges. Pyramid workouts are also great to amp up your intensity and help you build more muscle. Below are 3 types of pyramiding sets that you can use.
1) Descending pyramid-decrease weight, increase reps
* First warmup properly before starting your first set. You will then start off with the heaviest weight you plan to use on the first working set. You should aim for about 5-6 reps on set one. Each set after you should decrease the weight and increase the reps. On your fourth set or so you should be around 15 reps.
2) Ascending pyramid-increase weight, decrease reps
* First warmup properly before starting your first set. Start off with lighter weight and do around 15 reps on set one. Each set after drop the weight by about 10-20% and do less reps. So set two might be about 12 reps or so. By set four you will be using the heaviest weight yet and doing around 4-5 reps.
3) Triangle pyramid-combining the above two
* This routine involves more sets, and the higher volumes helps you to build more muscle. Start by doing the ascending pyramid in which you use light weight and high reps. Go all the way down to about 4-5 reps and then now try and work your way back up. Most likely you wont be able to hit the same reps so make adjustments and get as close as you can.This would look like this: