For how to choose your Lubricants, I think these points are essential: low resistance, appropriate viscosity, no damage to the plastic, long-lasting lubrication and less likely to attract dust.
For the method of use lubrication: do use too much Lubricants, as well as only lubricating the areas of friction. because friction is mainly happens between the core and the base. One part is between the protruding part on the spindle and the metal sheet on the base, and the other part is between the bar projections on both sides of the spindle and the corresponding two slides on the base.
These is some advise for those who don't know too much about mechanical keycap keyboard or new to here.