How do I paint silver plated light fixture

Best paint is Rustoleum for that project, and many colors to choose from. Just do light coats.

clean, sprat paint with Rusteoleum 2x for metal

When you say silver plated, I think the object has real silver on the surface. If so, I think paint would degrade the item's value. Just because an item is old does not mean it is junk. If, however, you are sure the surface is just shiny metal then go for it. Below is a link with steps for spray painting. Skip steps at your peril. In addition to paint not sticking properly, you could end up with spray paint drifting onto a floor.

http://milescityacehardware.com/the-tips-tricks-of-great-metal-spray-painting/

Ty