Well it was more than clothes for me, I was a skinny guy who wore wal-mart jeans and shirts, or band t-shirts all the time. Had a really generic buzzed on the sides, one inch on top haircut. Didn't really pay much attention to skin-care or grooming.
I've been bodybuilding for five years now, I'm not a super flashy dresser but I make sure everything fits well and matches etc. I'm not a complete metrosexual but I buy some grooming products and keep everything looking neat.
Huge change in reaction from everyone, walking around in jeans and band t-shirts people treat you like a kid. If you walk around well-dressed and present yourself with more confidence people show you so much more respect.
It's about the attitude you develop too, Just today I had a bit of an argument with a secretary at school, she was giving me attitude about something when I had just went in and asked politely so I flat out put her in her place and told her that I was treating her with respect and expected the same in return, it shut her up and she complied, I don't think I could have pulled that off dressed like a slob.