For oval shaped faces, applying it slightly below your cheekbones, sweeping it from your temples (just below the corner of my eye works best for me) to about an inch away from your mouth and nose typically looks best, keeping a relatively light hand.
This is the best diagram I could find that didn't have other pictures, and
this, this, and
this are all good examples of people wearing their blush like that. It's best to try to avoid bringing your blush too close to your nose or else you might end up looking like you have a cold or a sunburn. (My mom does this all the time and she ends up looking like she has a cold.)