My daughter always puts herself down. She's very caring and smart, and I compliment her all the time, but nothing seems to work. – Mike
Helping her see that others, like you, appreciate her qualities is a great start. You can also try to get her involved in activities like volunteering that encourage cooperation rather than competition. This will give her a taste of success and will show her what she is capable of accomplishing.
Most everyone has some self-doubt from time to time, but if your daughter's self-criticism is interfering with her life, a trained therapist can help uncover the reasons for her low self-esteem and suggest ways to improve it.