Specificity is the concept of strength training the specific muscle group that the performance is desired in. For example, if you need strong legs, arm curls will not help. Specificity also refers to the type of training. For optimal increases in strength, the individual needs to use heavier weight with fewer reps. If the athlete needs to enhance endurance, then lighter weight and more reps are specific to their needs.
Rest is a variable that is widely overlooked.
Training day after day will reduce the amount of repair that can occur and reduce the gains that can be had from most forms of training. A muscle should not be trained with resistance on consecutive days. Only perform one set the first week and slowly progress to three sets. Use a range of 8 to 12 reps for each exercise. If you can lift the weight more than 12 reps then the weight is too light.