While you do not need to be a professional bodybuilder or elite athlete to reap the benefits of weight training, you do need to know proper techniques to see results and avoid injury.
Lift an appropriate amount of weight - If you are new to weight training you want to choose a weight that you will be able to complete between 12-15 repetitions, while focusing on form and technique.
Use proper form - If you are just starting out with a weight training program, you'll want to get advice from a certified fitness professional. A lot of times people tend to do exercises they see other people doing in the gym. However, a lot of times they are not being executed correctly. Learning the proper way to perform an exercise is extremely important when lifting weights to avoid injury and to see the results you're putting the hard work in for.
Breathe - It is very important to breathe while you are lifting weights. You want to breathe out as you lift the weights and breathe in as you lower them.
Balance out the muscle groups - If you're working one muscle group, for example, the chest, make sure you work the opposing muscle group which would be the back. This way your focusing on a total body workout and you will be less likely to create muscle imbalances which can cause overuse injuries.
Rest - You want to avoid working the same muscle groups two days in a row. It is a good idea when starting out to work the major muscle groups two to three times a week.
Skip your warm-up - Cold muscles are more prone to injury. Warm up for 5-10 minutes before starting your weight training routine.
Rush - Take your time while performing your exercises paying close attention to your form, technique, and breathing.