I always spray, roll or brush a bonding agent (Link or Plasterweld) into cracks or old plaster edges before taping. I embed the tape (paper for corners) in a setting-type compound, like Durabond 90 (sets in 90 mins or less). So the second coat can go on the same day. For second coats you can use another setting-type compound, Easysand (setting time @ 90, 45, etc), or regular green-lid drywall mud. Finishing touches with regular mud, for ease of sanding. Since it's a ceiling corner, it would be all right to use the dust-reduced type of mud, which I do not recommend for general work as it is very soft, but at a ceiling it wouldn't see any rough handling. It could, of course, all be done with ordinary green-lid mud, but I have had a great track record with durabond for old plaster repairs.
Casey

I have been told that fiberglass tape is better for a plaster and drywall joint.I would do all else exactly as sombreuil posted.

The biggest problem with joining to old plaster is that it sucks moisture out of the compound so rapidly the setting compounds do not set correctly, and the pre-mixed mud does not stick to it very well, even with e bonding agent.

I use a bonding agent to cover large ares of old plaster, but getting it into a crack is so hit or miss it is rarely worth the trouble.

If you dampen the old plaster then wipe off any surface water after about 5 minutes the new setting compound will not get sucked dry and will set up properly.

For a small crack a hand spray bottle set to create a narrow spray (almost a stream) to get into the crack works well.