I think being well dressed is over rated. It can also backfire on you. If the girl thinks you spend too much time on your appearance, or she keeps getting well dressed men trying to get her attention - being another well dressed man is going to bore her.
More important than being well dressed is to disarm the girl. Being well dressed might impress her, but it may put her on her guard.
There was this highly desired girl I knew who guys were constantly hitting on all the time. Guys constantly were offering her things, inviting her places, getting dressed up when they knew she would see them, etc. One day I contrived to run into her, and purposely dressed in old jeans and a normal white shirt - and it wasn't even ironed, and a pair of sandals. There she was at the cafeteria and I sat down next to her with my food, she was with her girlfriends. As I was sitting myself down, all the guys around looked to see who was sitting next to her. I chatted her up for awhile, invited her to a movie, and then we dted and became a couple.
All it took was being bold and direct, and not caring about rejection. She was taken by surprise, and I won the big prize.