Work quickly and efficiently and won't make the job stretch out to cost you more. Do a quality job - he won't be slapdash in order to hurry through it.
Prepare all surfaces thoroughly and not just cover-up problems.
Offer his expertise when choosing colours and suggest schemes within your budget.
Take control so you can relax while he gets on with the job and leaves everything clean and tidy.
Charge you a fair price with no need to worry about unexpected extras.
Advise of surface faults and other problems as the job progresses.
Always take pride in his work because he is going to be around long enough for you to recommend him to others.