If the paint is sound them Just apply a diluted coat of PVA to the wall (enough water added to the PVA to provide a milky consistency). Ensure any loose paint is scraped off first.
If the PVA dries really quick then the suction may be too high and a 2nd, possibly even a 3rd coat of PVA may be needed to ensure the plaster does not dry out too quick.
Then plaster as normal.
If the PVA dries really quickly - so will the plaster, so either keep your eye on how quickly the PVA dries (if it dries within 15 minutes then consider applying another coat or do the suction test to confirm.
If the suction is properly controlled a lot of potential problems will be eliminated.
Beginners: When starting out your arm may not be use to all the physical work. A lot of pressure is required on the trowel in the later stages - so you can make it easier for yourself by applying the PVA the previous day.
Normally it is good to apply the plaster when the PVA is tacky - so if you're intending to let it dry, then put a handful of soft sand or finish plaster in with the PVA solution. Then when this solution has been applied and left to dry - a rough sandpaper like texture will result, to which the plaster will adhere to nicely.