The Principle of Specificity maintains that if you want to see specific results, you should perform exercises that are specific to those results.
For example, if you want to increase your bicep strength, you should perform bicep exercises. If you want to run a 5K race, you should train by running. If you want to improve in a specific sport, you should perform exercises that are specific to that sport.
This principle, though simple, is important to keep in mind if there are specific results you want to see from your workouts.