I take it from the service light question you're talking about the new/BMW mini?
I wouldn't do spark plugs on a small service unless it needs it-also I would check to see if they are platinum plugs if so they don't need changing as often as normal type spark plugs-but when they do they are very expensive, but its your choice and you won't do any harm by fitting a set if they're reasonably priced.
If you're doing a small service then just oil, oil filter, check all lights and fluid levels and tyre pressures etc, check air filter (I think from memory there are two types of air filter) as it won't do you any harm to check...unless you somehow break something, I'd check the pollen filter too as they often get overlooked. I'd prob just have a quick glance at the state of the brakes-is there enough meat on the pads left?-you can be caught out as you might not be able to see the inner pads, and check the discs-are they excessively worn? any lips around the inner and outer areas where the pad makes contact on the disc and is there any really bad/deep scores worn into the disc?
This is by no means a comprehensive check list as you can tell and its up to you how far you want to go, what did it have done last time and how long ago was it-thats what you should ask yourself.
I'm the service manager in a garage by the way!
