You might consider doing some research into positive affirmations. I find them very helpful. Another tip would be to eliminate the word "immature" from your vocabulary.

Since you have not provided examples, my general advice for improving your behavior and verbal interchanges with others, since this seems to be your goal, here are a couple of positive affirmation to say every day, in the morning and also whenever you get the chance (privately, to yourself):

I can think before I act.

another might be:

I can listen politely to others.