Try changing things up. Lift heavier weights for 6-8 reps and cut your rest to 20-30 seconds. If you are doing a complex movement like a squat, instead of doing a short rest period like I just described, superset another lift in to keep moving while giving your legs adequate rest. Shrugs are a good example of a quick movement you can do in between squat sets. That will up your intensity and shock your body by using a heavier workload.

And as has been stated, diet is probably the most important facet of this game. Get your diet dialed in. Having a good definition to your body involves more than eating fewer calories.