Using Free Weights
Although free-weight exercises provide the greatest degree of movement freedom, this advantage can be a liability. An increase in the possibilities of how you can move a bar, dumbbell, or weight plate means an increase in the number of potentially hazardous circumstances.

Load bars properly.
Take great care to load bars evenly and with the proper weight. If the ends of a suspended bar (where it is resting on the upright supports or rack) are not loaded evenly, the bar may tip, possibly resulting in injury. Learning to recognize the weight of different bars and of weight plates will help you in loading the bar evenly and in placing the proper amount of load on the bar.

Lock barbells and dumbbells.
Lifting with unlocked barbells and dumbbells is dangerous. Weight plates that are not secured with locks can easily slide off the bar and land on your feet or other body parts. Before performing every set of exercises, you should check both locks for tightness. Do not assume that the last person using the barbell or dumbbell tightened the locks.

Avoid backing into others.
Take care to avoid backing into others, because an untimely bump may cause a barbell or dumbbell to fall on your head (from an overhead exercise) or face (from a lying-down or supine exercise), on the head or face of someone training nearby, or both.

Be aware of extended bars.
Extended bars those that overhang or extend outward from machines (like the lat pulldown exercise), barbells supported on large racks (like on a squat rack), bench uprights, or bars held in the hands of other people who are working out. Pay special attention to bars that are positioned at or above shoulder height; serious facial injuries can result from walking into them, so be careful!

Store equipment properly.
Each piece of equipment in the weight training area should be stored in a special location. People can trip or slip on barbells, dumbbells, and weight plates that are left unattended or not placed in their proper locations. Make sure that you put your equipment away immediately after using it, both at home and away and you are working out in a fitness facility. If you have children at home you may face an added danger if they are able to climb on equipment or try to lift plates and bars that are too heavy for them. Secure weight training equipment so that children do not have access to it without your supervision.
Using Machines
Although the mechanics of lifting on a machine are less complicated, following a few steps will help ensure safe lifting:
# Always select the correct load and insert the T- or L-shaped selector key all the way in. Do not use type of key that does not come with the specific machine.
# Adjust the machine to accommodate your body size, and refer to signs or illustrations (if provided) for the location of the adjustment knobs or dials. If placards do not exist or are not sure how to make adjustments, request help from a qualified person.
# Establish a stable support base when performing exercises that involve positioning your feet on the floor or positioning your head, torso, hips, or legs on or against the equipment.
# Fasten seat belts securely (if provided).
# Perform exercises through the full range of motion and always in a slow and controlled manner.
# Do not allow the weight plates to slam against the rest of the stack during the lowering phase or to hit the pulleys during the raising phase.
If a piece of equipment doesn’t work properly, ask for help. Never place your hands or fingers between weight stacks to dislodge a selector key that is stuck, and keep your hands and fingers (and long hair!) away from moving chains, belts, pulleys, and cams.

Warm up and cool down
Preparing the body to weight train is just as important as doing the actual workout. Without a warm-up, you often will not be able to lift as much, and even attempting to lift will not feel comfortable. Following your workout, you need to decrease your activity level gradually to let your body rest and recover.

Warm up The warm-up is an essential part of any well-conceived weight training program. Warm-up activities raise the body temperature and increase blood flow to the muscles, making them more pliable and less likely to become injured when challenged to contract against heavy loads, Activities such as walking, jogging, stationary cycling, stair climbing or stair stepping, rowing and rope skipping are excellent general body warm-up exercises. Another type of warm-up involves performing the exercise that you are warming up for but with a very lights load for 8 to 15 repetitions. This specific (versus general) type of warm-up provides the opportunity for you to get your brain and muscles working in harmony before you tax them with heavier loads. This type of warm-up also gives you the chance to acquire a better sense or feel for which muscles are involved and how to get them more involved in the exercise. Once you have completed 10 or 15 minutes of general warm-up, consider performing a set of 8 to 15 repetitions before the first actual set of an exercise. The Combination of both types of warm-up will prepare you mentally as well as physically for the training session.

Stretch
You should include stretching activities for each major muscle group and several for the lower back at the end of the warm-up period. Stretching is more successful after the warm-up than before it because muscles are more flexible and more easily stretched when they are warm. Be careful when performing stretching exercises; otherwise, you may injure yourself. Follow these guidelines as you stretch:
# Move slowly into the stretched position and stretch to a point where you can feel tension, not pain.
# Relax, Breathe in deeply, and then exhale
# Hold the stretch for 15 to 30 seconds and then return slowly to the starting position.
# Perform each stretch at least twice