How to Build Pectoral Muscles Safely
Pecs
The pectoral muscles are your chest muscles. They are used when you bring your arms in front of your chest and when you bring your shoulders forward. Building up the pecs can benefit both men and women by making their chest look bigger and firmer. For men it can make them look and feel stronger. Injuries to the pectorals are rare but they do occur sometimes when people like weightlifters strain them too much. Pectoral injuries are very painful and take a long time to heal. So you should build pectoral muscles safely. Don't be too hard on yourself.
While working out don't focus on your chest for the whole workout and don't ignore pain and muscle fatigue. After a difficult chest workout give your pectorals a day off before straining them again.
Do a variety of chest exercises instead of doing the same one over and over again and make sure you can do at least 6 reps at a time. If the weight is too heavy then you could easily injure yourself. Sets of 8 to 12 are good for building your strength.


Push Ups
Push ups are a good chest exercise that you can do almost anywhere at anytime. You just need to drop down, assume the position and start doing push ups. It is easy to modify the push ups so they focus on the muscle area you want. Wide grip push ups put more strain on the pectorals. Diamond push ups are narrow push ups that focus more on the inner pectoral muscles. Incline push ups focus on the lower pectoral muscles. Decline push-ups focus on the upper pectoral muscles. When doing an incline push up you raise your upper body. When doing a decline push up you raise your feet. You can use a chair or a set of stairs to raise your upper body or legs.
Explosive push-ups allow you to use more force. You push up hard and fast causing your hands to leave the ground while your arms are still extended. While your hands are in the air you can try to clap your hands together and then getting them back into position before landing back on the ground.
Dips
Get a pair of sturdy chairs and place them back to back shoulder width apart. Place a hand on the back of each chair. You are grabbing the very top part of the chairs. Next lift your knees and support your body weight. To do one rep slowly lower yourself down by bending your elbows until your lower and upper arm reach a 90 degree angle. Then lift yourself back up so you arms are straight again. You can put something on the chair seats to reduce the chance of them accidentally moving and put something on the back to make it more comfortable for your hands. You could replace the chairs with two couches or anything else that would work.
Ball Throws
Lie down on you back with a ball in your hands over your chest. Then throw the ball vertically with both hands so it goes straight up. Catch it when it comes down and do it again. Those are lying ball throws. If you have a partner or a wall then you can stand and throw horizontally. Only use a wall if the ball is meant to be thrown against walls. When you throw the movement should be similar to an exploding push up. Try to use a ball that has some weight to it like a medicine ball.
Boxing
Your chest muscles are the used while punching and blocking. So boxers get a good chest workout while they are boxing. They also work their pectorals when they shadow box or punch a punching bag. If you punch a punching bag or the air with power then you can strengthen your pecs. Boxing workouts can firm up your abs and reduce fat while adding some variety to your chest workouts.
Bench or Floor Press
Lying on your back and lifting a barbell or 2 dumbbells up and down is a lot like doing push ups but it is more dangerous. You can do bench presses or floor presses. The width of your grip should be a bit wider than the width of your shoulders. Doing them on a bench allows use to do them at an incline or a decline. An incline bench press focus on the upper chest muscles and a decline bench press focus on the lower chest. While using dumbbells you can change to a hammer-grip with palms facing inward. Try to use weights that you can lift at least 6 times.
Most people don't have a good reason to lift weights that are so heavy they can not lift them 6 times. It just significantly increases the risk. Having a spotter makes the exercises a lot safer and easier. If you are using dumbbells the spotter can pass them to you and take them away when you are done. If you are using a barbell then they can help you lift the weight if you have trouble completing a rep. Lifting one dumbbell at a time makes it safer by allowing you to help yourself out. You can grab the dumbbell with your free hand and set it down with both hands. That is what I do when I do floor dumbbell presses by myself at home with a heavy dumbbell.
A lot of weight lifters think bench presses are essential for building pectoral muscles. Weightlifting exercises like presses can be a very effective way to work you chest muscles but they are not essential and they are not as safe as bodyweight exercises. You should be able to increase the size of your pecs just by using your body. So the dumbbell and barbell exercises are optional.
Pullovers
You can do pullovers with a barbell or a dumbbell. Lie face up on a bench. Your head should be hanging over the bench so the bench does not interfere with your arm movements. Lift the barbell or dumbbell above your chest with your arm extended but bent slightly. Then move the weight behind your head in a downward arc as far as you can before arcing the weight back up into the starting position. A stability ball can be used instead of an exercise bench. Move slowly and stop going down when you feel you have reached you limit. For this type of exercise it is important that you use weights that are not very heavy. They should be lighter than the weight you lift while doing presses.
Dumbbell Pullover, Incline Press, Decline Pull-Up
Dumbbell Flyes
Flyes are similar to presses. You lie on your back and hold a pair of dumbbells close together above your chest with the palms of your hands facing each other. Your arms should be extended with the elbows slightly bent. During the exercise the elbows stay locked in that position. Slowly lower your hands out to your side until they are at shoulder level. Then slowly raise them back into the starting position. Repeat multiple times.
Doing it on a flat bench works the whole pectoral area. Changing the angle changes the focus like it does with bench presses. The exercise works the upper chest more when done on an incline. When done on a decline it works the lower chest more.

Sports and Other Activities
Chest workouts are not the only way to build muscle. There are sports and other activities that work the pectorals. If you are moving your arms in front of your chest then you are working your chest muscles. Some activities that work your chest are kayaking, canoeing, rowing, swimming, tennis, baseball, sweeping, and raking.
Exercises that don't focus on the chest muscles can still make your chest look bigger and firmer. So can a healthy diet. Slim down by getting rid of fat and firm up your abs. It will make your chest look more defined. Activities like walking, running, biking, rollerblading and jumping rope would help.