If the paper face has been pulled off your Gyprock sheets, you should start by scraping away any of the flaking paint that is no longer bonded to the surface beneath and remove any remaining lifted paper.
Once the loose flaking paint has been removed, apply a shellac-based primer such as Zinsser 369g B-I-N Primer Sealer Stain Blocker Aerosol to the patch prior to applying your topping compound. It will help the plaster stick and prevent moisture transfer that can cause bubbling.
After priming, you'll need to apply a skim coat of plaster to the areas where the paper has been pulled off. This can be done with a 250mm Taping Knife and some Easy-Finish Topping Compound. Apply a thin skim coat, doing your best to avoid leave lines or heavy edges, to all areas where the paper has been removed.
Once dry, you will need to sand it smooth using a combination of a 120 Grit Angled Sanding Sponge and a Plaster Hand Sander.
Once smooth, you can apply a coat of primer before painting with your choice of interior paint.
You might like to have a look at How to paint like a professional for some further guidance. - JacobZ
