Sometimes when you’re feeling down on yourself it’s easy to forget all of the things you are good at, so prepare in advance. Write a “confidence resume”, where you make a list of all of the things you are proud of. It doesn’t have to just be professional accomplishments or things that are generally considered impressive. Make it about the things that you feel good about. It’s helpful to break it down into categories. I break it down into accomplishments, personality traits, and genuine compliments people have paid me in the past.
An important next step is to add looking at it to the reminder system of your choice, either on your calendar, boomerang, bulletin board, or other reminder system. This will only be useful if you remember to look at it periodically and remember all the ways you’re awesome.