In the past 2 years I've learned that the way I dress reflects my self confidence. Before I go to bed every night, I lay out which suit or set of business clothes I am wearing tomorrow. That method does two things: Buys me a few minutes of time I would normally waste in the morning looking for clothes to wear and it also gives me something to look forward to (basically jump starting my day).
I like to be overdressed no matter what occasion or event I'm attending. Now, I'm not saying for you to go out and buy some crazy expensive suits and business clothes, but spend your money on looking the part because that helps fuel your confidence of being the part. Please note, I am not a psychology major, nor am I college educated. But I've learned that when I put on that neatly pressed dress shirt, polished up shoes and tighten that slick tie I bought myself, my confidence level is boosted beyond comprehension.
When I walk into a client's office and I'm better dressed than them, I feel that I have the upper hand even if I don't but that helps me make courageous decisions when I ask for their business. Other business professionals will respect the way you dress. My favorite quote is "Dress like you own the bank, not like you need a loan from one." and that couldn't be anymore true. The dress clothes you wear should fit your build. If the suit is a little too big or too long, have it tailored. If you just spent $400 $500 or $5000 on that suit, complete the picture by tailoring it to fit you. Look the part, be the part and own your confidence.
AND: Know that when people see you all dressed up, you'll hear "Oh, what are you so dressed up for?"... My response is always "I take my life seriously."
Remember that the way you dress is for you only. Be great.