I can't agree enough with the recommendation the book "The Non-Designers Design Book." It's been around in various editions for over fifteen years, and has been on more designers, coders, and IAs bookshelves than I can count.
I'd like to share one more design "secret" that every graphic designer knows, and everyone can start using in a matter of minutes: The Grid.
Most designers work with an invisible grid that all of their elements live within, or sometimes break out of. It can be any size and ratio you want to make it. If you begin with a grid system, you'll be able to get as creative as you want with your layout, and things will fit together better and just "feel right" when you're done.
The best book I've found about grids is The Designer and the Grid http://amzn.to/lYAcyQ
You can also go to http://www.thegridsystem.org/ which actually lives up to its subtitle of "The ultimate resourcein grid systems."
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