If you’re a beginning or intermediate LaTeX user, you can probably produce pretty nice looking documents as long as the document is one of the standard types. If you want to produce slightly unusual documents—a homework assignment or résumé, say—you’ll need to find (or write) a new document class that supports that type of document.
The LaTeX Templates site may be just what you need. They have all sorts of templates along with examples of what the result looks like. Once you’ve chosen one you like, you just download and put in your tex directory. I use their templates all the time and have found them very useful. Take a look at their examples and see if there’s something you can use.