First you need to mechanically remove any laquer, dried machine oil, grit, whatever that may be left on them. Use 0000 steel wool, rubbing them well. Do this off the bass. Fix the ball end into something solid, then grab the tuner end and steel wool them very well. You wont hurt them with a lot of pressure. After that, use a rag to wipe off all loose residue including steel bits. After that, if you wish, you can use whatever you like as a lube, if you even need it. I've use plain hand lotion, mineral oil, or whatever. You might not want or need lube at all. Some ppl think that step will damage the strings. It wont any more than years of handling them with greasy hands.
The smoothing step with the steel wool is the most important and effective thing you can do.