I don't use the turntable.

I set my scanner on a tripod.

I set the distance to the object by looking at the middle cross that is projected, to be in focus.

I put talc on my object and distribute it evenly with a brush.

I overlap my scan a lot, maybe as much as 50%. Make sure there are overlapping distinctive features in your scans, create some if needed by placing your object on a cardboard and cutting shapes into it.

With this I get clean scans almost every time.

Last tip: after a scan, if you see holes in the model, apply more talc on the hole before you start the next scan.