If you have a good ear for melody, and can 'hear' the tune in your head, start with the bass chords, and add the melody, not the other way 'round - which hardly ever works in anything other than a perfunctory fashion. In fact I'd always recommend this, even if it means recording the melody without the bass and playing it back while you find (by trial and error in my case) which sounds best. Then go back to the right hand and make it fit whatever you've decided for your left hand. This invariably works pretty well, it's amazing what you can do with the bass end when you don't have to worry about the melody. This might then mean re-thinking the right hand and doing some cross-rowing. Cross-rowing tends to present a psychological, rather than a physical barrier, but since (again, in my case) I feel, rather than look at the buttons, I hardly know when I'm crossing rows, and in any case after a short while everything begins to become automatic; your right fingers intuitively find the buttons that match the bass end. I'm sure there'll be dozens of other techniques however, but that's my 'two penn'orth'.
