Mr Bowie's Ashes to Ashes!

[Nelli]

What is this song about, particularly the finishing lines 'my mother said to get things done, you'd better not mess with Major Tom'?

[Buffy]

This is really just a guess, but I thought "Major Tom" was slang for a drug, most likely marijuana. So mother is telling son to stay away from drugs.

[Buffy]

Me again -- or it could be LSD.

[bobbobley]

or it could be reference to his character from Space Oddity, who was so hard that when he found himself floating in a tin can, far above the world, with his circuits jammed, and nothing he could do, still managed to get back to earth. You wouldn't therefore want to mess with him.
that bit wasn't chronicled in the song of course due to its lack of poignancy but its a well-known fact.