I am very insincere. I don't think about it beforehand and regret it afterwards. After making a decision, it's easy to go back on our word and lie. How to correct this?

First, learn to be sincere and control yourself from telling lies. Second, think twice. Think more about what you can't decide. You can talk to your parents and friends, and they can give you some advice, so that you won't easily regret your decision.