There are a lot of opinions on breathing technique.
Some say... Just breathe. Your body will adjust naturally. In. Out. Repeat. Use your mouth, your nose, and any other way you can get air.
At first you may feel like you're not "breathing right." That you're struggling, can't get a good breathing rhythm going, or just feel constantly out of breath. This is normal. Over time (a few months or so) this will go away. Many runners naturally fall into a rhythm of breathing in for 2 steps and out for 1, or in for 2 and out for 2, etc. Whatever feels most comfortable for you is what you should do. The method you use will generally not affect your performance as long as you're getting enough air. If you're constantly gasping like a fish out of water, it's not because you're breathing wrong, it's because you're running too fast. Slow down. You can increase your speed after you've built a good aerobic base.
If you run too fast and breathe too hard... You might get the dreaded stitch!!
Remember that for comfortable runs you should be able to run and carry on a conversation at the same time. If you are having trouble breathing you MAY be running too hard or too fast.
Sometimes breathing cadences can lead to foot injuries! It seems that some runners emphasize their foot strikes on inhales or exhales, and the advice to counteract the negative impact of this over-emphasis is to run with an uneven cadence, something like 2 breaths in and 3 breaths out.
Most experienced runners agree, however, that cadence breathing is only for full out, end-of-the-race running. Most distance running, including all training (except perhaps speedwork), should be done with relaxed, whatever-comes-naturally breathing.