If you want to gain muscles fast and easy you should make sure that the resting time between the sets on each exercise are as short as possible. Bring a timer with you if it’s helpful and set it on maximum 1 minute. By not resting more than this long between sets you optimize the work out for the muscles and they will send signals to the body to build more muscle tissue to be able to put up with the training. The weights you lift should be just as much so you can bear to do between 6-8 reps and then have a short rest before your next set. Three sets on each exercise is often the best number. In this way your body will be programmed to build muscles more efficiently.