Improving your footwork in tennis will significantly decrease the amount of errors you make. The split-step is one of the most important aspects of footwork. It is also one of the most overlooked. It may seem like a small movement but it will make a significant difference to the way you play. Even the best players in the world spend time practising their split-step!
The split-step is a small jump (just a few centimetres off the ground) where both feet land in roughly the same position as to where they started. You should start your split-step as your opponent starts swinging their racquet through to hit the ball. When you land, your weight should stay a little forward with your knees slightly bent so you can push off explosively in the direction of the ball.