====Clean and lubricate the precision steel rods====
(This is for the unthreaded steel rods.)
You can clean them with WD-40. Apply to clean rag, then wipe.
Remove the WD-40 //completely// afterwards. Get another clean rag, wipe it off thoroughly. WD-40 is bad for bearings.
Diego says you shouldn't have to add any lubricant. If you do, a high-quality machine oil such as 3-in-1 should work. Also see
[[http://reprap.org/wiki/Lubrication|here]].