If I'm in doubt how to lubricate a joint, first I clean it thoroughly, which is sometimes (quite often, actually) all it needs, and then as a first attempt at actual lubrication I may use a light touch of dry graphite powder, as sold by locksmiths for instance.
I won't put a wet or oily lubricant on anything important until I know it's the correct thing to use.
And, as said above, WD40 is not a lubricant - it's for driving out moisture on metal parts, both for storage and to help ease jammed joints.
Paul