There is a separation of exercise needed to get big, defined muscles.
To build muscle size you use fewer reps and increase the weight as you get stronger.
For definition you don't increase the weight but add more reps. You could also add a cardio routine to help burn the fat for faster results.
You should never lift fast or jerk the weights. Always maintain proper form and lift in slow steady movements. If the weight is too much for you to do this lower the weight a little. If you’re lifting fast or jerking the weight you’re only cheating yourself.
My advice is if your at the size you want to be at don't increase the weight but start doing more reps. If your doing sets of 8, move to sets of 10 or 12. Also start running, even if it's only 3 days a week. You can alternate the days you lift with the days you run for better results.