Trying to rehab tired plaster ceiling need help please
You'll want to use a setting type compound, like Durabond, for the initial "fill-in" coats. Then regular joint compound is OK after that, in multiple thin coats.

Wet the old plaster prior and during the first coat, with a well wrung sponge, or mist it with a spray bottle. Don't soak it, just get it damp.

On the finishing coats, you don't have to get it wet, but do allow plenty of drying time, between coats, and wipe any sanding dust off, between coats with a well-wrung sponge.

Do not put regular joint compound directly on the old plaster - it will dry out too fast, shrink,  and fall off. The interface layer of "Setting Type" (I use Durabond 90, in the bags), is required, if you plan to finish with "All-Purpose" premixed joint compound.

Note: It is entirely OK, and recommended, to work in small sections at a time - don't try to get it all done at once, or even in one day.