Clean the tester with a little alcohol (the store should provide this in a spray bottle) and use a test brush or a cotton swab to apply the color to your lips. If you don't want to apply the tester lipstick to your mouth, test it on the pads of your fingertips. Your fingertips are closer to your lip color than your wrist or the side of your hand. Otherwise, you will be mixing multiple colors together. Ask a sales rep for makeup remover or lotion.  Look for a shade that, worn with no other make up, brightens your face and makes other makeup unnecessary. Sometimes it's hard to objectively judge what looks best on ourselves. A professional at the makeup counter can match you with the right color.

How would you rephrase that briefly using Vietnamese?
Thử son trước khi mua. Lau sạch màu son cũ trước khi thử màu mới. Mua son ở nơi có ánh sáng đầy đủ. Trang điểm ít hoặc không trang điểm khi thử son. Đề nghị giúp đỡ tại gian hàng trang điểm.