It always drives me crazy when someone comes up with a brilliant idea or does a great job on a project—then discounts any acknowledgment of her achievement by saying, "Oh, it was nothing." It wasn't nothing! And if you act like you don't deserve praise, then who are other people to disagree with you?
Your confidence can be affected by the way that people you respect salute who you are and what you do. (There's a reason we call it "a vote of confidence" when others give us a pat on the back.) I'm not suggesting you let everyone else determine how you feel about yourself, but it sure doesn't hurt if someone you care about thinks you have a commendable trait. Being able to receive constructive, positive feedback can help counteract negative thoughts and build confidence. Besides, if you respect someone enough to take their criticism to heart, it's only fair to also accept their praise. If you can't stop yourself from brushing off compliments, practice saying this in front of your bathroom mirror:
"Thanks. I appreciate your saying that. I worked really hard, and the fact that you noticed means a lot."