It is not that complicated. It is not easy, but it is simple.
Accept yourself as someone worthwhile. Do not go around feeling like you are not good enough. You are here for a reason, and your job is to figure out where you can make a real contribution.
Take total responsibility for what you are and what you become. That means no blaming others, and no excuses.
Learn to forgive, both yourself and others. Holding on to anger and grudges never built anything good. Let them go.
Be careful what you feed your mind. Do not waste time on mental junk. Pay attention to the things that help you become a better person.
Set solid goals and work toward them. Know what your values are, and stick to them.
And take care of your body. Everything else depends on it.