Research is your friend. Find out what companies there are in your area and what their ratings are. When looking at those comments, it's good to check the most positive comments as well as the most negative. That way you can see what the range of experience were with a particular company. That's my opinion anyway. http://skg.net.au/services/commercial-cleaning/
I would surf the web and do some research on different commercial cleaning companies in you area. I'd read reviews on the companies and find out how they can serve you to see which one would be your best fit. You could also look through phone books as well. I'm sure you should be able to find something that will work for you.
I would just put yourself out there and try to make yourself different. Personally, I like to look for cleaning that has gone all "green" because I love the environment. I would also try word of mouth because that's where I hear a lot of things. Good luck!