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With foundation application, it's best to know first what product works; for an oily skin a water based foundation is best and for dry skin for instance an oil based one might be best. For wear one should consider coverage; full, medium or sheer which usually depends on the state of the skin.
Note that if the skin is blemished or plagued with breakouts it shouldn't be masked with foundation but be treated first -in fact most times it's best to let the skin breathe by staying off makeup to help clear those areas of the skin- before proceeding with foundation and the rest of the face makeup.
Foundation should sit 'skin perfect' on the face meaning it should blend seamlessly into the skin and other areas as the hairline, ears, neck area to create a perfect canvas for other makeup product.
Whether using a foundation brush or beauty blender, product (foundation) should be worked into the face in gentle strokes in a way where it's pushed in gently into the skin.
With the foundation brush gently work around areas of the face for seamless coverage pushing product into the skin in a downward stroke where when applying with beauty blender, product should be pushed in gently into the skin in short dabbing strokes.
Note that If wearing a light foundation, you can build up application to get a medium or full coverage effect or till the desired coverage is achieved.
With these you're on the way to apply foundation flawless and without fuss daily!