If there is one mistake that nearly all creative professionals are culprit of, it is this.
They make promises to clients, and then they don't deliver on them.
They tell a client "I will have that to you tomorrow."
Then tomorrow rolls around, and they break the promise. They don't deliver. This broken promise upsets the client and it hurts the relationship.
The key is not to work faster.
The key is to under promise, and then over deliver.
If you think you can get something to the client by tomorrow, tell them 3 days from now. Give yourself a buffer.
If you get it done tomorrow, then the client will be ecstatic. But if life comes up, and it takes longer than expected (as it often does), then you have two more days to deliver.
Yes, it may mean the client waits a bit longer, but you are making a promise and keeping it.
Taking your time is better than breaking a promise.
Don't make promises you can't keep.
Under promise, over deliver.
Never the other way around.