Breathing while running - newbie

I use to run cross country in high school and I think the key to preventing lung-and leg-fatigue is breathing more fully. When you take deeper breaths, you use more air sacs in your lungs, which allows you to take in more oxygen to feed your muscles.
One way to make the switch easier is to work on belly breathing when you're not running, and the skill will eventually carry over to your running.

This!

When I started running I would even practice belly breathing while watching TV! By moving your belly, rather than ribcage, out when breathing you really pull the diaphragm down, getting plenty of oxygen into your lungs. Yoga exercises are good for learning this, if you have a chance.

I prefer to breathe through my mouth - only got a little nose and can get more air in through my mouth (which, some people would say, is too big!).

I also time my breathing when running - so try taking long, slow, steady, deep belly breaths rather than short gasps from your upper chest (so easy to do when feeling out of breath and exhausted). I usually do a count of five for each breath in and out.

And... when I started running I was constantly gasping for breath and thought I would never get to grips with it. But I have - and so will you. It's perfectly normal to be struggling a bit at first - you're learning a new skill and once you've got it you will have it for life. Not to mention your heart and lungs will adapt and get stronger, so helping your breathing.

If I think about my breathing, it gets all kind of messed up.

What works for me is to run at a pace that slow and controlled enough that I could mouth the words to whatever music I'm listening to.

Lip readers would have a field day with me.

Forgot to say - heavy breathing through my mouth also warns people strolling along in the park where I run that I am coming up behind them and going to overtake them (verrrrryyyy slowly as I shuffle past!)

I did Track/CC in High School with asthma I didn't know I had until college, so I know breathing sucks.

I usually go with music or only as fast as I can get oxygen in.

As far as a trick to use is 1-3 quick breaths in to fully expand your lungs then a slower controlled breath out to keep breathing from getting too sporadic or wheezy.

Congratulations on starting C25K!

My suggestion for you is to slow down, and run conscientiously while breathing ... take into account how you're breathing as you're taking each step and go at a nice easy pace to start. You don't want to push yourself where it feels like its too difficult to breathe, but you want to feel like you need to "catch" it. In time, your body will get used to it and you'll be able to regulate your breathing better as you train. Good luck!