It would be a good idea to have your attorney draw up the contract for sale in order to satisfy all the legal requirements of a contract sale and purchase.
You would then collect the payaments, provide the purchaser with an annual interest statement, and report the interest received as income on your tax returns.. (see you CPA or accountant for details.)
If you still currently have a mortgage loan on the property, you could not sell the home on contract due to the fact that your mortgage lender could call the loan due on demand becasue of your title status transfer.
Or, you could turn the home into a rental property and rent it to your friend until he can qualify for a loan. (Remember, there is no such thing as "Rent-To-Own"... The correct term is lease with the option to purchase).
Hope this helps.