What I mean is this - don't let your customers run your business. I have a client who turned some work over fairly quickly for a client. The client however, was not quick in responding. When the client finally did respond, she requested a follow up meeting on a day that my client really wasn't available.
Instead of telling her client that she was booked, she tried to fit her in - and then felt the frustration of having too much to do in too little time.
In business, while the client is always right, they aren't always prompt. It's not your responsibility to change your schedule to accommodate theirs. You can't feel their time frame more than they do.
Be clear about when you are available and when you aren't. That will help your clients schedule themselves accordingly. And it is their responsibility to take ownership of their needs - not yours.
At the same time, if you are clear about the 'scope of work' you'll be performing, how long it will take, and what it will cost, then the client knows when they are inside - or outside - of the parameters. It will be easier to let them know when you are available, instead of trying to always be available. It will also be easier to let them know if the project is going to cost more money when they change the 'scope of work.'
When you have clear expectations of how your business will run, your clients will fall in step with them.