This FAQ doesn't recommend any specific product. Products may be identified as examples.

DeOxit is a resin-flux cleaner for solder joints.

Tuner Lube is a conductive lubricant made specifically for pots and fader wipers. Tuner Lube also works on jacks, but it doesn't soak in so well and will attract dust, and you've got a big mess from the overspray to deal with if the jack is mounted in the amp when you squirt it.

Zero Residue Cleaner is for cleaning up the mess DeOxit and Tuner Lube make when oversprayed. DO NOT spray anything but Zero Residue cleaner on tube sockets.
You don't want anything soaking into ceramic sockets or sitting on the surface of plastic sockets attracting dust and shorting your tubes with arcing. Unless you just love a light show.

ProGold is a metal treatment (soaks into the metal) made for the plug and switch contact points, like Cliff jacks. ProGold is also good for dipping tube pins into. If you need to get ProGold into the tube socket's pin receivers, just dip the tube's pins in ProGold (spray a little in the cap for dipping) and use the wet tube pins to lube the socket's pin receivers. Dip twice and reapply twice. That way there's no overspray problems.

Spray every Cliff or Switchcraft jack with ProGold before you test each one in an amp. They'll still need the occasional maintenance squirt every few months, just like any other jack.