Acne can take a serious toll on self your esteem. Going to see a dermatologist is the first step to curing severe acne. But if just have a few blemishes, or just gets a spot occasionally, then proper makeup application can do the trick.
Find a concealer that is oil-free. There are specific concealers meant to cover acne and that contain an acne fighting ingredient such as salicylic acid or benzyl peroxide. Dab on the concealer gently with a concealer brush, let it set for a minute, and then blend out the edges so you don't see where the concealer meets the skin. Don't brush too much directly over the spot - you don't want to brush all the concealer away! After the concealer is blended, set it with some loose powder.
For more apparent blemishes, find an oil-free medium coverage foundation. This will help camouflage large problem areas, and tone down redness caused by the inflammation of the acne. Use a clean foundation brush to apply the foundation every time, and set with oil-free loose powder. Don't use your fingers or sponges to spread foundation as they harbor bacteria and can make acne worse.