See below. You can do positive self-affirmation. You can also make an inventory of your own self -- what makes you a good person; what can you do well, or skilled at. You can also set up small goals for yourself to do during the day and do the summary at the end of the day -- will help you with the sense of accomplishment, which helps with self-esteem.
Self Esteem. You will need to uncover how you came to doubt yourself in the first place and then develop strategies to change your story to a more realistic view of yourself. Consult with a clinical psychologist and read the updated articles on depression and anxiety on the soundimindz.Org web site. Best.
Do. The best way to improve self-esteem is to identify a goal you consider worthy--usually it is something challenging, and something you perhaps fear failing at--and then pursue it. You may or may not succeed. Regardless, your self-esteem will become solid for having given it your all. If you do succeed, you will have the added pleasure of success. But the joy of trying is always the greatest.
Be good, and learn! There are many ways to have healthy self-esteem. Most agree that there are two broad components to self-esteem: (1) the view that I am a worthwhile or good person; and (2) the view that I have some competence (i know things or know how to do things). If people continue to strive to be virtuous or good and to learn and develop skills they will tend to have a positive self-concept. Striving is key.