It can be a hard item to select but the point of it is to bring color and brightness into your face after the application of a foundation. Regardless of age or skin tone, a liquid/creme blush or a powder with an iridescent sheen do the job best. Both will help to reflect the light off of the face and thus camoflaguing the appearance of fine lines/blemishes. A matte finished blush will add color but not give a glow so this should especially be avoided for more mature skin or blemished skin.
COLOR:
You should select a shade that is most similar to your current cheek color when you are flushed. After working out, look in the mirror to see what color your cheeks are- if they are pink, go with a pink blush, if they are reddish, go with a blush with more red undertones. If in doubt- find the blush that has both pink and coral undertones (much like this font color) and you can't go wrong! This shade compliments light or dark hair, warm or cool skin tones and brings life to any face!
Another important tip: PLACEMENT:
For younger faces, it is perfectly acceptable to place the blush on the apples of the cheeks. For more mature faces, the blush should be swept just above the apple of the cheeks to help give height to the cheekbones which may be less apparent as we age.
Less is always best but if you happen to get too much: no need to wash your face and start from scratch- use some pressed powder over the area to make the color less noticeable- added benefit: it will help your makeup stay fresher looking, longer!
[caption id="attachment_51" align="aligncenter" width="300" caption="Reese Whitherspoon's Perfect Blushing Complexion"]

Most importantly, blush means very little if you don't smile!!!