Plastering upside down is definitely an art and there are more than a few of us who have retreated beaten with ceiling plaster stuck to us like dough. The job becomes even more complicated when the ceiling has complicated detailing, and that is definitely a case where you need to Find a Plasterer if you want to remain sane.
If you still want to try your hand at this then the trick is to understand that plaster has to be exactly the right consistency, and that nothing sticks naturally the wrong way round. If you fiddle with it after you have managed to get it to stick, the chances are good that it will come loose again and frustrate you to the point of getting Plasterer Quotes. in other words, it its working, don’t try to fix it.
The key is to establish a basic surface over as much of the area as possible, and then to leave things be, while the material semi-dries. After that you can fill in any gaps, and tidy up any difficult corners. When you have done that, and scratched the surface carefully, you are ready to attempt the second coat.
The second coat should go easier because the existing surface and the new plaster over it are more compatible. Aim to add an even layer that conceals everything beneath it. After it has dried to the right consistency you can gradually work off the surface with a straight edge until you have got it right.
Personally I do not think that this is a job for an amateur to attempt. If you do manage to get it right though, then your next step could be to become a Plasterer in London – that is assuming that you are a glutton for pain.