When training, be sure to GRADUALLY increase the intensity in order to avoid injuries. Do not increase the frequency, duration, or intensity of your training too quickly. Follow the "ten percent rule". Do not increase the level of your training more than 10 percent each week. Also, do not ONLY focus on strength training. Along with building muscle strength, which is a vital component of any work out, also incorporate all other aspects of fitness, such as endurance, cardiovascular fitness, and flexibility. This will round out your training and provide the most long term benefit.