The first few times you try this exercise, you may find it challenging to keep that even breathing pattern through the progressively faster intervals. Keep practicing.
When you're ready to try it with a "real run" begin by running at a slow pace. Focus on belly breathing as you take in a deep breath. Then release this breath with a good exhale. To make this easier, try inhaling over three strides and exhaling over three strides, making a complete breathing cycle six strides. There are no hard and fast rules.
Depending on your stride, your inhale may take two to four strides and the exhale may take two to four strides (the inhale and exhale stride count doesn't have to be equal). Remember, a good long exhale will clear the lungs of CO2 making room for more O2. If associating your breathing with your stride doesn't work for you, try counting — one, two, three, inhale; one, two, three, exhale. With practice, this will become second nature and you will no longer need to count or keep track of strides.
Whichever technique you use, the main goal is to control your breathing so that you're breathing from your diaphragm or "belly breathing." Controlled, deep breathing will help prevent those annoying side stitches too. Belly breathing gets more oxygen into the blood stream, increases lung capacity and endurance. Once you have your breathing under control, you'll experience more enjoyable runs. You'll also be able to then focus on increasing your speed and/or distance.
After practicing, if you're still experiencing "tight lungs" and you feel like you're unable to get in enough air, check in with your doctor. You could be experiencing sports-induced asthma.More: 4 Ways to Stay Positive Through Injuries Sign up for your next race.