When weight training, it is very important to use the proper techniques in order to gain maximal benefits and reduce unnecessary injury. In other words, quality is as important as quantity...if not moreso. While free weights are recommended over machines, familiarize yourself with the exercises and how to properly adjust the machines to be used before beginning.
Breathing
Proper breathing is very important during resistance training. It is recommended to inhale during the lowering (eccentric contraction) phase of the movement and exhale during the last two thirds of the lifting (concentric contraction) phase. Holding your breath during the first thirds of the lift stabilizes your ribcage and shoulder girdle which may increase lifting capacity. The main point of breathing during an exercise is to NEVER hold your breath between repititions (valsalva manuever).
A well-designed strength training program incorporates different phases for different parts of the season:
Introductory Phase - to orientate the beginner or senescent athlete and prepare them for the strength phase