Before you put on a drop of foundation, apply a primer on clean skin—it will help blur imperfections so your skin tone looks more even and you won't need as much makeup. I like Giorgio Armani Beauty Light Master Primer, which has blue and pink light-reflecting particles to help diffuse discolorations. Squeeze out a pea-size drop and apply it over your entire face using a clean foundation brush. A word of caution: Avoid those green-tinged primers and concealers that are marketed to counteract redness. They're too tricky for most women to master, and applied incorrectly, they can make the skin look ashy.
The texture of your foundation is also key. Skip anything with shimmer, which can make redness appear more obvious. Instead, choose a semi-matte or satin formula such as Giorgio Armani Beauty Lasting Silk UV Foundation. Pump a small amount on to the back of your hand, then pat a small dot of the makeup on each cheek, one on your forehead, and another on your chin. Using a foundation brush such as Giorgio Armani Beauty Designer Foundation Brush, blend the makeup out toward the perimeters of your face. The brush gives you more control than a sponge or your fingers by allowing you to reach the crevices around your nose and other features, and it also buffs the color so you get an even application.
If, after applying your foundation, you still see a few red blotches, cover them with an opaque concealer that comes in a pot or stick, such as Dermablend Quick-Fix. With a small concealer brush, stipple the makeup on the area, then use feathery strokes around the edges to blend them into your skin. If you have several glaring red patches, cover them first with the concealer, give it a few minutes to set, then apply your foundation—this will help prevent you from applying too much makeup.
To help your foundation and concealer stay put, set everything with a light dusting of translucent powder just on the areas where you tend to get shiny. But keep in mind: Red blotches tend to also be dry, and applying powder on dry skin can cause it to cake and magnify the problem. So make sure your skin is well moisturized before putting on any makeup.