If there's one piece of advice I can give to designers who are in the early stages of developing a relationship with a client it's to set up expectations for your client that are realistic! I abide by the laws of wiggle room, and I always under promise and over deliver!
If you think it will take you 3 days to finish a project then tell your client it will take 5 days. When you deliver it in 3 days they'll be impressed, and on the off-chance that you get sick, have a computer glitch or take an unexpected day off you will have created some wiggle room for yourself to ensure you still meet your deadline. Keeping your clients happy can be as simple as setting realistic expectations and then delivering up a slice of brilliance :)
