You need a tax identification number and you have to know how to bid. Each item you have to take out of the place is so much $ per item.
If you have to take it to the dump you have to estimate how many trips and multiply the dump fee by that amount.
Then if they want you to clean the house and do repairs and painting that is a charge above the clean out.
Check with Real estates, landlords, banks and brokers.
With landlords often they don't want to clean out and clean up after the last renters especially if they were evictions.
Check with the Small Business association in your area to find out the whole process of licenses.
Small Business Administration - Small Business Planner