Inhale on the less strenuous phase of the exercise, and exhale on the more demanding phase of the exercise. Upon LIFTING inhale, DROP exhale.

If you're hitting heavy weights, you inhale on the easy part, hold you breath for just a short second as you approach the hardest part of the exercise (commonly called the "sticking point"), and once you've completed it, you exhale per usual. The maneuver helps you tighten your core muscles and maintain proper form. However, it does briefly increase blood pressure. So if you have any cardiovascular problems, the move isn't for you.

Continuous breathing will help you to increase nitric oxide, an important gas that relaxes the arteries and keeps the blood flow that you need to sustain your rhythmic activity. Establish a pace and then match it with your breathing. If you can talk without huffing and puffing while running then your pace and breathing is good. 

While it takes some serious concentration at first, apparently the greatest running impact occurs when your foot strike coincides with the beginning of your exhale. So by keeping a 3:2 breath tempo, you'll minimize your chance of injury.

Stretching is all about loosening up—so focus on inhaling deeply. It relaxes your muscles so you can get a better stretch and lower your risk of pulling anything. Just like stretching breathing exercises are important after a workout as they help regulate your heart and your body after putting it under some strain.

Ever finished a set of squats, thought "that wasn't so bad," and then started huffing and puffing? That's because your body needs oxygen to replete its energy stores. So in between sets of exercises, do breathing exercises. 

Diaphragmatic breathing is what most recommend, it  allows you to get more oxygen into your lungs—and to your muscles—per breath so you can hit your next exercise hard. To do it, focus on filling and emptying your abdomen with each breath rather than raising and lowering your chest