I can tell you that people come back for more when they see new things. It's a simple idea, but it works. We recently put it in a Media Database which carries movies, sounds, wallpapers and more, which did bring in more visitors than normal. Other than that, keep people coming back with regular news updates, new features, new tutorials, whatever your site is based on do more of it. Basically, if you want to improve the success of your site you have to keep visitors coming back for something. If they see something old, chances are they aren't going to visit again, if they see that you've updated then they'll keep coming back to see what you've got for them. Other than that, there's the age old saying, "Keep it simple stupid," I've learned that cluttered sites or sites with TOO much information are useless to visitors. If they want to get something, they want it fast, they don't wanna search around your site for hours.
Programs I use: Dreamweaver, Photoshop, Paint Shop Pro & many books/resources for coding if necessary