Picking your DJ is like picking what to wear, normally you don't grab the first thing in the closet. 
(Unless of course you are a clown...or Lady GaGa LOL ;-) )
Most couples meet with at least 2 suppliers per category before making a decision on their wedding so it is a good thing to have a few questions prepared. This article hopefully will give you some ideas on what to ask your potential DJ.
- How long has your business been running for?
- How many years have you/your DJs personally been DJing for?
- How many weddings a year do you do?
- What kind of equipment do you use?
- What do you wear to my event?
- What happens if you get sick?
- What happens if your equipment breaks?
- How early do you set up?
- How long does it take you to set up?
- Is set up/pack down/ meetings all covered in your costs?
- What lights do you bring and is it included?
- What deposit is required?
- When is the balance due?
- What is your cancellation policy?
- Do I get to meet the DJ who will be doing my event?
- What if we absolutely DO/DO NOT want certain songs/styles/genres played?
- Can guests make requests?
- Can you MC the night?
- How much experience have you had as an MC?
- Can we please have a contract?
- How quickly do you respond to emails/phonecalls?
- DO you have any recent testimonials?
A good DJ company (like Komodo Music ;-) ) can answer all these questions with confidence and ensure any other questions you may have are easily dealt with.Whenever you leave a meeting, make sure that you feel confident with the DJ company you have chosen :-) 
(Photo courtesy of "dancemusic.about.com")