Two Separate Questions
First, how much of the old texture should be removed? Second, what work is needed to make the remaining ceiling look uniform?
Choose the Practical Route
On one project, most texture may come down before relatively minor repairs. On another, aggressive removal could cause enough substrate damage that partial removal followed by resurfacing becomes more practical.
Prepare for Light, Primer and Paint
Smooth ceilings reveal surface variation more readily than textured ones. Repair, sanding and inspection need to be completed before the final coating stages.
Related ceiling work
The useful next step depends on what the ceiling reveals. Read about ceiling skim coating, repair after texture removal, primer and paint, or the factors covered in the cost guide.