Use a stud finder or tap along. When you suspect you have a stud use a thin screwdriver of similar and punch through the wall to check you do indeed have a stud.

Their bits might suck but I did manage to pick up one of their sets for cheap on a sale and for the odd time I need something that I don't otherwise have they are useful.

Yep, I had this done before moving to my current place and am now finally getting around to repainting each room in turn. I got quotes for a few options, this skim coating over the popcorn, putting new drywall below it, and full scraping/removal and then skim coating. This was the cheapest option, though adding an extra layer of drywall wasn't much more - but it would have lowered the ceilings perceivably, whilst the skim coat is really only taking off maybe 10mm from the total height of the room - totally unnoticeable.

Colin Furze is one step ahead there.