When exercising, pick movements that require the use of more than one joint.

For example, consider the bicep curl. Only the elbow is moving so only the muscles around the elbow are working through a range of motion. Now consider the row. The elbow is performing the same movement as in the bicep curl, called flexion (the wrist is getting closer to the shoulder) but at the same time the shoulder is moving as well. This exercise uses the muscles around the elbow as well as the muscles around the shoulder.

Multi-joint exercises: more work, less time.