ALL: how often you clean and re grease or oil your vise always depends on use and even more so the type of use.
one thing i try to do when cutting, filing or working on my vises where there might be debris hitting the slide is to put a rag (clean or oily) on the slide to catch any debris. then pull the rag out when you are done and shake it into your garbage can. this will keep a lot of debris out of inside of your vise and keep the slide and screw cleaner.
i've picked up some vises off of a guy's bench where he might have used it every day for 30-50 years without ever greasing it and they still perform, but they do like a little grease and oil especially if used fairly often.
simple thread title and good subject cause a lot of us don't take care of our tools we spent good money to buy.
if you want to eliminate surface rust there are several spray on and rub on oils and waxes to use and i like BLO. Fretters made up a little recipe for his humid shop's tools in England that he's still perfecting, but might be something to protect your vise and steel in your shops.
The recipe for that graphite paste.
1oz beeswax
30ml gum/pure turpentine (2 tablespoons)
60ml linseed oil (4 tablespoons)
3 rounded tablespoons of graphite powder
The method I use for making it is to get a saucepan and roughly half fill it with water, (just make sure the water level is not high enough to flood over the lip of the jar when you put that in there), put the jar containing the ingredients into the water and then set that pan off to simmer. Mix the paste occasionally as the wax melts. It'll eventually turn completely liquid, so give it a good stir once it does and then remove the jar from the saucepan of water and stand it to one side to air cool. Once you notice the top starting to skin over, give it one last thorough stir to stir up the graphite powder and then leave it to harden fully. Once it's set, time to have a diddle with it.
Leave the top on the jar when you're not stirring, btw. Don't tighten the lid down fully until after that final stir, but keep it loosely on there as much as possible. It'll prevent the turpentine evaporating.
You may want to try tweaking the formula to best suit you, btw. I've just settled on this blend as it seems a good compromise of softness but without being too runny.
cheers