If you want to paint your spokes, then you would want the easiest way. Otherwise replace them with stainless ones.
So take the wheels off and clean the spokes with steel wool or a scourer pad. Any surface rust that you can't remove, even the tiniest pits you will need to treat with a rust convertor. I would use a good quality urethane enamel (preferably with a rust inhibitor) and brush it on.(Unless you want to mask everything up)
Keep in mind if you pressure wash your bike, it could get ugly. I de-chromed my Harley by sanding the chrome and painting it with satin black and gloss black urethane enamel in a pressure can. It has held up well for a couple of years now.
Companies like POR15 have a lot of good products, but you could end up spending more than a set of new spokes, unless you have other uses for it.