What kind of mistakes can a new meditator in his/her early 20's avoid?
Choose the middle between all extreme contrasts.

If you are going too fast, go slower.

In your meditation you might choose a kind of meditation.
Then you would try to keep yourself on doing only that one thing you have choosen.
You would be disturbed by thoughts or feelings and might not keep yourself on one point.
This is OK. This is meditation: if you come back from things which disturb you, back to point you have choosen. - Many people might think they do not meditate if they can not keep themself on one point - that is wrong.

I think you allready know you need patience, but also there might be a time where a change can help.