Drywall compound and tape make drywall hanging very forgiving when it comes to gaps.Naturally,the smaller the gap the better for both walls and ceilings.I have seen some bad jobs where the Gap was 1/2 an inch or so,however,with enough coats of compound you can still fix it.For first time drywallers,I'd say be more concerned that the drywall edges are at the same level because uneven seams are trickier to fix than gaps.Hope this helps.

Thanks so much for responding. I really needed to know these parameters.