Please don't use pencil dust or graphite powder - this WILL cause problems later on!!
Wd40 is perfectly fine to use as its silicone based & will evaporate & coat the pins. If this doesn't remedy your problem, the circlip of plug fixing screws have come loose or worn. I have 30 years experience as a locksmith. Hope this resolves your problem!
Regards.

Spraying any liquid is likely to have an adverse long term effect on the springs in the cylinder. Graphite powder would be my choice - and Garry has provided a recipe to make your own!

Wd40 tends to gum up the internal mechanism after a while. Get a standard HB pencil and keep rubbing the nib onto a piece of sandpaper or matchbox, over a sheet of paper till you have a small amount of "pencil dust." Then repeatedly coat the key as much as you can in this dust. Insert into the lock and push back and forward. Do this till the lock begins to ease.

Gary is correct with WD40 not been good. You need a silicone spray or furniture polish.

Graphite powder normally leads to a build up of muck over time it is only a short term solution. WD-40 is a cleaner but removes any sort of lubrication you have in a lock so not recommended. just get some lock spray or a lubricant spray it will clean the lock and lube it up. And as above if the cir clip is loose or worn it can make it difficult to pull the key out. The best way of telling if that is the problem is to press your finger on the inner (where you put the key) then pull the key out. If the key then pulls out easily it is probably a problem with the cir clip.

you need to get the barrel changed before it seizes all together and becomes really difficult to remove

Don’t use wd40 as it’s just a degreaser it would work but can clog up the lock over time, you want to use a lubricant and cleaner like GT85