It really is a matter of practise, practise, practise. The best way is to know the song to sing first, then try accompanying it later. That way, there's less chance of the accompaniment pulling your voice away from the song. Accompaniments that follow the melody line are, for me, easier to sing to - rhythmic accompaniments that cut across the tune confuse me. That's why I gave up guitar for concertina, but maybe I'm just weird. Don't be put off - you've got to play and sing badly for long enough to become good. So play badly some more. Otherwise you'll never get better.

Good luck in your music,

Andrew