Appreciate yourself. If you're hard on yourself all the time, you'll make life hard for yourself. You don't deserve all that constant negativity and while it is important to focus on what needs self-improving, this should not be at the expense of your self-confidence. Tell yourself you're a great person who can do anything you put your mind to. Every time a negative or critical thought pops into your head, dismiss it with a positive thought that says "Yes, but I am healthy/clever/capable, etc." instead. Repeat this exercise regularly for best effect.