Depending on how fast you want to grow will determine which route you will take in gaining new clients. There are several ways of gaining new clients and here are a few.
Website Marketing (SEO
One of the quickest ways is website marketing, setting up a PPC (Pay Per Click) campaign with a major search engine such as google, bing or yahoo for your website. Although, I haven't had much experience with Bing. I received great response from google and not so great from yahoo. Although, PPC it is a little pricey it has been very successful.
This is door to door selling. Create a business card, flyer and/or brochure drive to a garden style office park (where each suite would be responsible to pay for there own janitorial service) and start passing out you business information. It helps if you have a coupon of some sort offering a discount on your services with an expiration date on the coupon.
There are several telemarketing companies that will get you leads for your cleaning company. You will either pay them by the hour or by the lead. This could be a great way to get customers without having to hire telemarketers and deal with all the administrative hassles.
BuyerZone is another source to get leads for your company. It is an online company that charges $17+ per lead but they send the same lead to five other companies in your area. The difference between companies like buyerzone and telemarketing services is that with a telemarketing service you do not share the lead.
Word of Mouth
This is a great way to get clients. Everyone you know should know that you have started your cleaning business and you are looking for new clients. Send an email to your friends, family and acquaintances letting them all about your company. Put it in your churches bulletin. Do what ever you need to get the word out.
I hope this helps!