Here are a few tips I've picked up through the years of trying to perfect the natural look.
Number One: Don't Overdo It
Go only slightly darker than your natural coloring with your makeup. (ie eyeliner and mascara) I use a brown mascara and eyeliner in my everyday look, as to not look overdone. Keep in mind that I have blonde hair naturally and my coloring is quite light, go with what you have.
Number Two: Blend
A person does not have natural sharply lined eyes (unless you're a cartoon character) so I always blend out everything including my eyeliner.
Number Three: Be Consistent
To achieve a natural look that will have everyone guessing if you're even wearing make up is to use the same products in all areas of the face. I will use my bronzer as my eyeshadow and contour to make sure my coloring is the same all around. This will also add a glow without giving too much away.
Number Four: Sponges Work Wonders
After I am done my face make up I spray my face with a fixing spray and press my makeup into my skin to eliminate that chalky look and bring a natural glow to the face. MAC fix+ has been my go to for years.
Number Five: Beat The Heat
Use some kind of finishing spray to keep your makeup in place all day. I use model in a bottle every time I know I'm going to have a long day. I've worked through 12 hour shifts and ran through the rain and my makeup didn't move an inch!