You need it to be somewhat tight. You want to be able to turn it somewhat, so you can get it up over the strings if needed (allows you to strum them still), but not so slack that the damn thing'll topple out.

You'll also want to be able to push it away from the strings for when you don't need it, as it'll just be in the way of things really normally.

Don't screw it up so tight it won't budge anymore and don't leave it widdling like a wussy where it'll fall off the second yer lad sneezes. Other than that, it's mostly personal preference.