My Quick Tip is to use your face foundation brush to buff the primer into the skin. If you don't have a foundation brush, a great and cheaper one is E.L.F Power Brush ( the studio line, which is the all black brushes). I use it all the time. It is only 3 dollars and you can find it at Target or online.
When you use the brush to buff in the primer, it helps to really smooth out the primer on your face. Also, the primer will prime the brush for the foundation so the foundation does not get lost into the brush. You are not wasting any foundation, which is always a bonus! It help to give you that airbrush look and finish, we all want and love.