I never let the engine sit for more than about 3 days without completely tearing it down. I take it out of the car, remove the clutch, airfilter, and pipe, cap the intake and exhaust ports along with the fuel inlet, give the outside of the engine a good spraying off with a nitrowash type spray cleaner. Then I completely tear the engine apart (I don't remove the bearings unless I'm replacing them), spray off every part to remove any fuel residue(which causes rust), inspect every part, coat all parts with Mugen engine maintainence oil(or similar), and reassemble the engine.
This does several things for me; I get use to tearing down engines, I can see any abnormal wear before it destroys the engine, and it gives me a good look at the burn pattern that clues me in as to my engine tune. I'm certainly no engine expert, but this has been working for me.
My 2 cents