Wear good clothes, e.g. a good shirt and a tie. Probably you should ask some girls what clothes they like a man to wear or you should go clothes-shopping with a female relative or a female co-worker.
Important note: A lot of women pay a lot attention to SHOES.
Don’t wear those clothes at all costs even when they are inappropriate or don’t suit you. Example: Don’t wear a tie and your new shoes while swimming. OK, this is an exaggeration, but imagine yourself going bowling and you wear beautiful but uncomfortable clothes that make you sweat? Or going to the movies with a Hawaiian T-shirt.
On the other hand (since you are looking for a girl-friend anywhere) dress well whenever and wherever you go. You go shopping? Shave and dress well! You go to an exhibition? Shave and dress well. You go to a football match? Shave and dress well!
Another important thought: Woman are usually very “clothes-aware”. In fact they communicate thru clothes and thru make-up (they wear shorter skirts and redder lipstick to show they are datable). Thus by wearing good clothes YOU establish immediately a communication line, too.