OK, I don't know what's professional and what's not. So I'll just tell you what I like to see.

The site you have a lot of white space so that it doesn't look cluttered and I don't have to spend too much time looking for information on a page. If I can't find something easily and I can go somewhere else, I will.

The same goes for the navigation structure. Don't do like Microsoft and have a zillion levels of navigation. That is so frustrating and when I don't find what I'm looking for after navigating a dozen or more pages, then I end up really aggravated.

Multiple links to pages are helpful. For example, if you have a fairly straightforward navigation structure where each path is it's own thing, you should still have links to other pages that are related, even if they aren't in the same path.

Avoid flashy things. They're distracting. Just because something is "cool" doesn't mean you should use it. Too many professional sites use gimmicks that actually make their site harder to use.

Avoid using every font in the book.

Avoid an over abundance of colors. Muted colors are good overall or bright colors if they are just a spot here and there.

If you ask for advice, don't slam everyone who gives you some even if you aren't going to use it. That happens a lot here for some reason.

Post your pages temporarily and provide a link so you can get feedback early before you put a ton of hours into it.

That's all I can think of off the top of my head.