Getting in touch with a few real estate agents and brokers in your area is definitely a great start. If there is a local investors club in your area, I would look for them online and have some fliers of business cards made. Investors buy property on a regular basis and some don't have crews that are dedicated to initial clean up.
Another important key to remember, since you are seriously considering this and I would like for you to make sure you look at both sides of the coin, is to keep in mind that some of these clean ups don't involve just a broom and some good ol' fashioned elbow grease. Some of these homes need extensive cleaning and many of them have large items that need to be removed. All of which may require large containers for trash removal, or a pickup truck to take certain items away from the property, etc.
Not to say that you can't add these costs to your prices, but it is something to keep in mind when talking to people who can use your services.
Another great idea if you want to get started and get involved with making contacts, getting testimonials and some good referrals would be to consider starting off by contacting property management offices in your area and let them know you do move-in, move-out cleanings, etc. These typically pay about $100 and up and it's a matter of giving the house a good cleaning before tenants move in or when old tenants move out.
You can easily work your way up to bigger jobs once you are more established.
Best of Luck!
I would already start looking into a business name (even if it's your own name), business cards and some type of web presence (i.e. website, Facebook, etc.)
I suggest you start by also offering your services to clean, trim, maintain homes to realtors. This is a service that no one is really offering and many agents may need. You can also do small home repairs.... fix ups to get homes ready to sell.
Here are some ideas: 1) go to the HUD website and register as a vendor 2) go to your bank branch and ask for the manager to give him or her your resume which can be just a letter telling who you are and what you want to do 3) contact real estate agents advertising foreclosures 4) contact waste removal services to see how they do business or have any leads for you 5) contact the small business government branch service to help you formulate a BUSINESS PLAN. I ADMIRE YOUR WORK ETHIC AND DREAM TO OWN YOUR OWN BUSINESS. GO FOR IT.