As you get stronger, you will eventually need to increase the resistance (aka the weight) that you are using. It is important that you increase the weight slowly and gradually. A 2.5 – 5 lb increase still constitutes a progression.
The second way to progressively overload is to increase the number of repetitions you do per exercise. Repetitions refer to the number of consecutive times you lift a weight for any given exercise.
In this situation, you use the same weight and the same rep scheme. You are increasing the volume by dividing the workload into more equal bouts. In general, I recommend doing no more than 5 sets per exercise for efficiency.
This forces your body to perform the same amount of work in less time. This will improve muscular efficiency, as your muscles have to overcome fatigue before starting the next set.