Use a utility knife to cut away any loose paper from the ceiling (Image 1). It should just peel right off. Scrape off the rest with a 6" putty knife.
Make sure to cut off only paper that is loose; the goal is to just cut what’s visibly loose and then patch it (Image 2).
Fasten as many screws as needed to the ceiling to secure the plaster to the lath (Image 1).
Use a drywall compound and a putty knife to spread a thick layer of mud over the screws (Image 2), after it is dry put on another coat. Mud the other patches and repaired areas with the drywall compound.
Sand down any excess drywall compound and then prime.