I attended graphic design in college. I can tell you the first things the teachers would tell us are basically Keep It Simple Stupid. More importantly, the content is the important part, so keep it practical while maintaining a good aesthetic. Too often people get caught in all the bells, whistles, and flashy stuff that technology allows. Try to keep to a minimum of two font choices, and they should complement each other. I am personally a fan of Optima and Tahoma. Seriff fonts are more easily read on paper, whereas san-seriff fonts are sometimes easier to read on a monitor. Follow a color scheme, possibly a traditional art one like complimentary, tertiary, etc. A great place to discover schemes that work together is Adobe's Kuler site, where you can set it to find different color schemes from one color you choose, and you can browse schemes other users have put together. One of the most important steps is to work "on the grid"; most any professional design is done on some sort of grid system. This helps you achieve repetition where need, but makes it all the more contrasting when you "break" the grid. A perfect example, which you have probably seen, is where most buttons and columns are laid out in a very rhythmic and "gridded" pattern, but there will e a jpeg resembling a polaroid near the top that is askew, or at an angle. This can draw attention. An example would be the items you have at the top of your page, like the D.L. and MP3 player. Keep in mind traditional art and design principles, such as repetition, symmetry, rhythm, contrast, white space (often underrated and underused!!), and size relationships of elements. Fonts should have a shape that complements the shapes around it; you may notice Times New Roman has very rounded ascenders and seriffs. Arial is very stick-like and straight, with little variation in the thickness in the "limbs" of the letters. Also, TRY TO AVOID FADDISH AND FLASHY FONTS!! They are far overused. Papyrus and brush scripts are an example. If you want to see some very classical design, check out Milton Glaser or Pentagram design. Try to make your columns of text have very smooth "edges", as in no words are sticking out far more or less than the preceding or next line. This can be achieved through CSS with font sizes, weights, and especially Kerning and Leading (respectively, the spaces between individual letters and words). And after you know the design rules, as they say, is when you can break them!
