This isn't a question we can answer: "attractive" is a subjective term, and what appeals to you I may find hideous, and vice versa.
And a lot of how to make it look good depends on what the application does: a music player will need a different "look and feel" from a business reporting app for example.
All I can suggest is that you start reading here:
Guidelines (Windows)[
^] and then look at how some of the other apps in the same area have done it, working out what you like and dislike about them.