When using blush and bronzer, it's most important to find a shade that suits your complexion. Generally, you shouldn't go too dark or too light--you run the risk of looking overly made-up, or having nothing show up. Some makeup companies like Maybelline or L'Oreal, have lines with specified blushes made for yout depth and tone of skin.
For people with warm (yellow or green) toned skin, try out peachy blushes, or tawny/brown blushes. Same goes with bronzers--stick with bronzers that are more golden, and less rosy.
For people with cool (pink or blue) toned skin, use pink blushes, or even lavender-toned blushes. For bronzers, try neutral or pinkish shades. Don't make the mistake of thinking pale = cool and dark = warm. Plenty of dark-skinned women have pink or blue undertones, and many light-skinned women have yellow, orange or green undertones.
As for placement, face shape is important here. Using blush or bronzer to contour the cheekbones is a great idea for people with round faces. However, those with more angular faces should focus on highlighting the apples of the cheeks, since contouring the cheekbones can make their face shape look too harsh. You can also contour a wide nose by running some bronzer down the sides of your nose--but don't go too dark--and make sure to use a matte bronzer for this, not a shimmery bronzer, which will highlight any bump or bone in your nose.