Everyone wants a solid number. In my mind, it's a situation-based measurement. I like to space my drywall screws closer than is prescribed by the books. True drywall professionals do not space their screws as tightly as I do. My defense on this is always: I'm not a pro.
The problem with close spacing is that you have even more drywall screw recesses to cover with drywall mud/compound. But if it makes you feel comfortable--and it does me--go for it.
FieldThe field is the inner section of your drywall; it's everything but the edges. The field is considered a more stable area, so the conventional prescription is to space the screws 12" apart.
I like to take the number a bit lower and space them about 8" apart.
In the left side of this photo, I needed to hold in the drywall a bit firmer, so I was spacing the screws as little as 6" apart.
EdgesDrywall edges are more prone to movement. You're trying to create a nice, tight seam so that you can tape and mud it over.
Close spacing of drywall screws on the edges can cause the edges to crumble.
The conventional drywall spacing for edges is 8".
You can space your screws as tightly as 5" on the edges, but even I would not go much tighter than that.