How to keep clients happy

People [get to] keep working [with clients]:

1) because their work is good
2) because they're easy to get along with
3) because they deliver the work on time

And you don't even need all 3! Two out of three is fine. People will tolerate how unpleasant you are, if your work is good and you deliver it on time. People will forgive the lateness of your work if it's good and they like you. And you don't have to be as good as everyone else if you're on time and it's always a pleasure to hear from you.

- Neil Gaiman