I found a great blog written by a local interior designer.

Some tips:

What to Look for in an Interior Designer

I do think it's important to have some kind of personal connection with a client. Communication styles have to mesh on a certain level, because it's important for both designer and client to get ideas and information across and to be heard. A larger project can take 9 months to a year or more. Life is short and you should like the people you are going to spend time with. This doesn't mean you have to become best friends, but it's helpful to have rapport.

In addition to design acumen, I think a certain amount of business sense is vital for a successful project. A designer should be good at management and should be professional, should return your phone call, should return your e-mail, should follow up with what they say they’re going to do. A client should feel they know what they are getting in an order and be kept abreast of scheduling. A designer should be able to get along with the other people involved in the project like the architect, contractor, etc.

Abbey Koplovitz - On Interior Design