Make a change. Identify the behaviors and situations that undermine your self-confidence, then try your hardest to change them. Stop hanging out with people who make you feel crummy. Instead of criticizing your reflection in the mirror, give yourself a compliment. Unresolved issues with other people or with God can weigh you down and trick you into thinking no one would love you if they knew the truth.
Confession is tough, but it's a cinch compared to living with guilt.
Read a classic novel. Start an exercise plan. Try a new sport, or pick up a musical instrument. Memorize a book of the Bible. In the process of collecting new experiences and finding a sense of accomplishment, you just might discover a talent you never knew you had.