Lubing the chain... hmm, I lube mine whenever it starts to squeak, but the main thing is to keep it clean (and the chainrings, cassette, etc the entire drivetrain CLEAN CLEAN!).
What do you mean by the rd (rear derailleur I presume?) moving around? How so? Describe it's movement because it could be bad (but fixable).
To clean an MTB, I assume your talking about dirt on the frame? I use a regular hoze with no nozzle without a lot of pressure so it's a little bit of water in a specific area which I then use a cheap rag to "scrub" and get dirt off. That way, nothing splashes into my perty teflon cable housings.
A routine check is something you should learn how to do yourself. Stuff like air pressure, brake pads, cable stretch etc is very basic and not hard to learn.
If you're talking about a full "tune-up" I take mine in every couple months because I simply don't have the tools to go over everything myself, but that can be mended with some cash.