I use Lock-Ease, graphited lock lubricant. As said above, you don't really want to use something wet, as that only attracts dirt. And you don't really want to get in there every week with WD-40.
Lock-Ease goes on wet, and gets the graphite down into the joint. Then the base fluid evaporates, and leaves the dry graphitye lubricant behind.
Amazon.com: AGS LE5 Lock Ease: Automotive