Not only careful communication is essential, but we would greatly recommend, when you pick out your type and brand of paint that you go and pay for it, with the contractor's discount, which is given by Sherwin-Williams and most paint companies. Then you will know how much paint you purchased and the coverage. If it is possible, inspect the work of the painter daily.
Thorough preparation is essential to ensure a good finish. Contractors might have to fill cracks or holes and remove old paint if it is badly worn, peeling or flaking. They remove all paint and apply a suitable primer to the bare surface. If the existing paint is in reasonable condition, they clean it and rub it with abrasive material to provide a key for the new paint. On new surfaces, such as bare wood or fresh plaster, they apply a suitable seal, followed by a primer coat.