Dear Jayant, hello..! Mainly the followpoints to be
1.The surface should be matured for minimum 3 months before painting.
2 Check for cracks and uneven surface,should be repaired.
3.For ceilings, POP work and basic electrification should be done before putty.
4.Apply a primer coat of White cement, If Cement based putty is to be done,
5.After required 2/3cots of putty &rubbing for levelling, Primer for emulsion should be applied.
6.now go for colour of your choice. Hope it is enough for preliminary job.....