Well, actually, it depends on your definition of tinsel.

If it's the yards-long ropes of shiny bottle-brushy stuff (what I call garland), then I put that on first*, but if it's the short, loose strands of shiny stuff (what we called rain when I was a kid, but is generally called tinsel or icicles) then that goes on last. *g*

*Second, really, after the strings of lights.