First thing you need to do is Incorporate. Get a lawyer and set up an LLC for the aircraft to offer you some bit of financial/liability protection.
Inspections and Maintenance - In addition to your required annual inspection you will also be required to complete a 100-hour inspection every 100-hours of operation.
Insurance - You will need a commercial insurance policy which allows you to rent the aircraft. This policy covers the aircraft, so you will also need (or at least want) general liability insurance and all the other trimmings that come with operating a business.
Everything Else:
Maintaining an adequate stock of "service spares" to maintain the aircraft. Tires, light bulbs, oil, oil filters, 5606 hydraulic fluid, etc. - As an individual owner you may be OK with being down for a week waiting for parts, but as a rental operation that will lose you customers.
Having a relationship with a mechanic to do the maintenance. Owner-Performed Preventive Maintenance goes out the window when the aircraft becomes a rental - you may still be able to assist your mechanic, but you can no longer do & sign-off on things like oil changes.
Vetting your renters - Are you a CFI? If not find one who will check them out.
Type up a set of rules and regulations to be handed out to prospective renters. If you like your plane and want it to stay in good condition you'll need to vet your renters. You want the kind of pilots who will police their trash from the cabin, fold the seat belts, lean the mixture appropriately, return the plane on time etc...
Set up a scheduling system - Holdshort.com is an online service that you can subscribe to and it also helps keep track of your renters pilots when their currency, BFR or certificates expire and alert you/them. Upload copies of their medicals and logbook BFR sign-offs.
Join AOPA. They will be glad to help you set up a flying club.
