For strength training, you should perform 2-3 sets of 6-8 repetitions. For endurance training, you should perform 3-4 sets of 8-12 repetitions?
For strength training, an ideal weight will make you very tired after 6-8 repetitions (ex. 60-80% 1RM). For endurance training, an ideal weight will make you feel very tired after 8-12 repetitions (ex. 40-60% 1RM)
In order to get stronger, you have to use a challenging amount of resistance and train 2-3 times per week. If the exercise is too easy, you won’t be able to build strength. A rule of thumb is to use a resistance that you can only perform 6-8 reps before fatigue.
For muscle hypertrophy, you should perform 2-3 sets with a resistance that is 80-90% of your 1-repetition maximum (1RM).
As a general rule, you should rest 1-3 minutes between sets. Shorter rest periods tend to build muscular endurance while longer rest periods tend to build strength.
There are plenty of ways to calculate a 1RM. One useful method is Brzycki's equation (1993). 1RM = Weight ÷ (1.0278 – (0.0278 × number of repetitions).