by colortwelve » 06 Jan 2013 11:35
Write a bassline first. Just bullshit a completely random bassline in some key. Then fill in the rest of the chord progression on top of it. Of course, you'll need to know enough theory to work with chords, inversions, and function, but that's relatively little material when you get down to it.
And just as a general guideline, I try to make my basslines move by step, thirds, or fifths. Any other interval tends to sound awkward (to me at least).