Learn as much as you can about the physics of sound. I can't stress this enough. If you don't learn this then you'll just end up writing average tunes (maybe not musically, but as far as clarity goes).
And practice!! you can't get good overnight, it requires years of hard work, similar to learning an instrument, although it's like learning 5 million different instruments. Read mags like Sound on sound and computer music, sometimes you gotta sift through some crap but there is some gems in these mags.