This may sound like an obvious answer, and it is. Exercise using weights and increase the amount and/or reps used over time. This formula will lead to an increase of strength as long as you stay consistent to your routine. Now a way to keep this process from plateauing is to mix up the variety of reps and weight. High reps like 10-15 help to improve your muscular endurance. Low reps like 5-8 with higher weight will help to improve your muscular strength.