If you are just graduated from schools, you may still dress like a student. If you are going to work dressing like that, you may look a little boyish or girlish. So that would be a problem.
There was a hot discussion about "How to dress like a man" on MetaFilter. And someone commented that to dress like a professional needs a lot of work:
1. Nice shoes. This is probably the biggest thing.
2. Jeans are fine, so long as they're nice jeans. Go to nice stores, go to vintage places, try stuff on - there are some very nice, very classy, very attractive jeans out there. There are also things like chinos that can look great in a more casual style.
3. In general, things that fit and that aren't threadbare.
4. For tops, honestly? You just have to shop. Again, try things on. Stores will have a huge variety of shirts that don't fit into the standard work vs. t-shirt vs. club shirt trifecta, so you'll just have to go looking. Sportcoats are great if the weather allows (spring/autumn).
5. Questions like this are why publications like GQ exist. They are, in many ways, noxious, but you can definitely look through the pictures for looks that you like. Try to figure out what's going on in those pictures.
6. Accessories. For men this principally means "a nice watch that matches the outfit", but things like hats, belts, other wrist accessories, etc. can and do all help. And honestly, the confidence to pick out and wear a masculine necklace for yourself is kind of rare, and I feel like it makes an impact for that reason.The more money you have to spend on this project, the easier it is. It's possible to look great on a budget, I've seen others do it, but I've personally never really managed it.
Someone suggested peeking at the Put This On blog and podcast. As for their own advice, many can't go far enough to recommend that a man pick up a nice pair of shoes—not your average sneakers, boots, or sandals, but actual shoes. There's a link proffered for this guide to matching shoes and jeans.
Handy stuff, especially for someone just getting out of school without a lot of guidance on how to dress. Women's clothing that "looks adult" is a lot more complex and varied, we've heard, but if you know of a good, simplified resource guide, please give us comments.