The most common mistake beginner runners make is to do too much, too soon.
Its almost inevitable. Seriously... don't beat yourself up up over it.
You start out and its HARD going. Seriously hard. If you're following a plan like the one I started with or the one I hand on to many others to help them get started you will start out running 1 minute or less with long walking breaks.
Then after a while, running feels good.
Seriously.. you can run.. you've gone from couch to 5k, or from nothing to 30 minutes.. or whatever it is and suddenly YOU FEEL GOOD.
At the start it seemed like it would never happen but... You ENJOY running.
Little side note.. as a scientist...
What has actually happened here is that you have developed a level of cardiovascular fitness. Your heart has upped its game and is now able to support this insane new activity you are doing. Your heart is AMAZING. Seriously.. just as a little test.. take something in your hand, a soft ball or a ball of paper or something, and squeeze it tight, really clench your fist.
Do this 100 times..
If you get to 100 and its still easy, keep going.
What number do you get to? 150? 200?
Perhaps the muscles in your hand and forearm told you to stop at 50.. or even 20.
That activity, that clenching, is done by your heart 60-80 times per minute every minute of every hour of your entire life.
Seriously incredible huh?
Anyway.. the heart is starting from a much stronger base point than your puny little skeletal muscles, so its probably unsurprising that when you start running, it can up its game a little easier than anything else.
Back to the main story.
So.. running feels good. So you run further.. you run faster.. and you can do it. you can breathe.. you don't collapse and puke or want to die.
You CAN do it.
Thing is.. you cant really.
The original limiting factor for a total beginner is the cardio fitness. After a while the limiting factor becomes the skeletal muscles... the legs.
So its highly common for people to push to far, too fast to the point where they get hurt.
2 days ago I went out for my first run in a few weeks. During boxing training (all 8 weeks if it) i did very little running.. probably less than 10 miles per week.
The other night I went out and i was feeling great. My cardio fitness was spot on and after a very brief warm up I started flying down the road... I was doing a 6:30 minute mile for a bit, then I caught myself on and slowed down to an equally stupid 7:30 pace.
I only ran 4 miles, but at an 8 min mile pace overall.
After a long break.. I should have been running about 2 mins a mile slower than that to give the legs some time to get back into it.
But no... I didn't.. I hammered it, ran too fast and guess what?
Yeah my legs hurt like hell today.
So.. in short.. try not to do too much too fast. Try no to hurt yourself... but don't beat yourself up when you inevitably do.