Plastering a wall with a skim coat of plaster should always be a last resort as it can add days to a job by the time the plaster has dried enough to be painted. This video shows how to prepare a badly damaged wall and make it look like brand new.
Firstly the wall is cleaned using a sugar soap solution, it is then filled using a quality filler. Once the filler has dried the wall is sanded before giving it another wipe down with a sponge and some clean water.
A mist coat of diluted non-vinyl emulsion can then be applied to the wall, once this is dry a top coat of paint can then be applied.