IMO the best exercise for defining muscles is the one called "pushing myself from the table." When you have a higher percentage of body fat it is harder to see the definition in the muscle, the leaner you are the more easily it is to see muscular definition.
Reduction of body fat is number one but the second best way to see more muscular definition is to increase the muscular size of the muscle therefore increasing the density of that particular muscle and as you get leaner the muscle will look more defined.
If you have a particular muscle that has plenty of size and density to it will appear more defined than if that same muscle is not as built up. So increasing the size of that muscle helps to improve density but it is secondary to the reduction of body fat.
The best combination of course is the increase in lean muscle tissue (density) and the reduction of body fat. If you do those two things together you will see improved definition in the quickest manner. Increase and shape in muscle comes from the ability to take a movement and put it through a full range of motion with greater intensity (weight), recovering from the workout (nutrition and rest) and then coming back to that workout again (4 to 7 days later) and being able to use more weight with the same form. Keep doing that over and over again and the increase in muscle will happen.
Kettlebells are excellent because it gives the ability to use full range of movements and of course use greater volume and intensity in your training. If you do not have access to things like kettlebells or other specialized equipment traditional weights and dumbells can still be used for the improvement in muscle definition.
The equation for muscle definition is simple.
Decreased body fat + Increased muscle = greater muscular definition
More Answers from Jeremiah Forster, NASM Elite Trainer