Here's what I did when I stored my Si.
- Fresh oil change. Oil lubricates the engine as well as trapping moisture and unburned fuel.
- Fuel stabilizer and full tank of gas. Fuel will deteriorate in as little as 60 days causing varnish deposits to build up in the engine.
- Lube all hinges and use protectant on all rubber seals (door, trunk, etc.)
- Box or two of Arm & Hammer baking soda to absorb moisture and odors in the interior.
- A large plastic tarp to park the car on. Concrete holds moisture and the tarp will provide a good moisture barrier.
- Disconnect battery, or get a Battery Tender http://batterytender.com/