Firstly it's all about what kind of look you're going for, do you want to look tanned or do you want to sculpt your face to give it a bit more definition?
If you want to look more tanned then the key thing to do is to apply the bronzer (can either be a matte bronzer or one with a bit of shimmer in it) to the high points of your face, so where the sun would naturally hit. For example to the cheekbones and around the edges of your forehead and nose. Make sure you use a fluffy brush for this (not a contour brush) and really blend it in, the more you blend the more natural it will look. Last point, make sure you have blended it into the hair line as well, otherwise it'll look like it's been plonked on your face and no where near natural looking!
Now i'm more of a contour kinda girl as I like to give my face a bit more shape, but also colour at the same time. Firstly, pick a bronzer that is completely matte so no shimmer what so ever, again, you want it to look as natural as possible. Next, i've done some little guidelines on the photo above on where to place a contour shade, first find the hollows of your cheeks by pressing lightly on the skin this is just below the cheekbone. Then either using a contour brush if you want a more harsh contour or a tapered blush brush if you want it to be more blended and softer. Then you apply it in a diagonal line directly below the cheekbone but don't go any further past the edge of your eye or eyebrow. Make sure you've blended it into the hairline and bam! you're done. You can also contour your forehead by applying it round the temples, and contour even more by blending it along your jawline. Oh and another one, you can contour your nose (I know it sounds crazy) but as you can see i don't really need to do that, but if you wanted to get a brush like the MAC 217 and lightly buff it down the bridge of your nose to make it look more streamlined. Again, I only really contour my cheeks!
Do any of you contour on a regular basis?