Remove everything from the garage. Don't make the job harder by forcing yourself to work around boxes, tools or cars.
Insulate the walls. This helps you maintain control of the internal climate in the room.
Hire an electrician to wire the room for lights, sound and air electrical units.
Finish the walls with sheetrock. This keeps the insulation in, covers all wires and gives the room a finished look.
Apply a relatively soft--but durable--floor covering. The primary choices are hardwood floors, epoxy, floor mats or tiles. Choose something that is forgiving when sitting, lying down or performing exercises.
Add mirrors, cabinets and other accessories as needed. Mirrors can be used to monitor your progress and form. Cabinets and wall hooks may be used to store towels, exercise garments and other equipment.
Bring the equipment into the room and arrange it for ease of access and use.