It would help to have contacts with a bank or other home lender. You might try contacting a few and asking if they need contractors who can clean out homes. I know a lady who started out doing lawn care for bank owned properties, and now she employs over 100 people, and all they do is turn around foreclosure properties.
There are likely some things they will want from you. Are you licensed? Do you have insurance to protect them and your workers? Do you have access to trucks, dumpsters and other equipment you may need?
many have been able to get started by contacting home builders, as well as real estate investors, many have unoccupied properties that need regular maintenance of landscape and minor repairs, once you get a contract with one of them than more offers will come your way. Depending on what state you are in, you will be able to grow your foreclosure cleaning business by contacting national companies who hire subcontractors.
There is a lot of good information you can find on the internet, learn as much as you can, it's hard work, but the pay is good. We started out by renting equipment in the beginning and that worked good for us and saved us some money. I left you a website we found a guide that gives you detailed information about operating and starting a business cleaning foreclosed homes www.dreamstreetinvestments.com