How to sand spindles on staircase?

Debt_Free_Chick

A bit surprised that wire wool wasn't mentioned until post #10 as that was my first thought.

Wire wool! And if you're only keying the surface, it only needs a quick rub over anyway.

WaveyDave_2

You don't mention how old your house is. If it is more than a couple of decades, one thing you need to be careful of is lead in the paint. If there is lead, you should not sand it, or if you do, you should use wet and dry paper, and keep the paper wet (rinsing often).