When applying blush it is very easy to end up with a line of color across your cheek bone. It may look nice from the front but from the side there is a very distinct line of makeup.
To avoid this I recommend only applying blush on the apple of the cheek and then blending with your fingers up and along the cheek bone. This way you still get the color and definition without the heaviness that using a blush brush would cause.
If you would like some help with application or color selection of blush, I would love to help.