Should I spray this makeup on the skin or do you advise I use a brush, sponge or other applicators?

There are no rules with regards to the Era makeup application. You can spray it on and achieve the airbrush finish, spray small dots on your cheeks, forehead, chin and blend, spray into sponge/blender and apply, spray into a big fluffy brush and apply, spray onto a palette and apply, spray into the palm of your hand and apply. Many users are fans of using a blender, however, use the application you are most comfortable with to achieve flawless coverage.