Given their intensly proad nature, when meeting a Hippogriff it is costomary to wait for them to make the first move. Be sure to maintain eye contact. You should always bow to a Hippogriff (This shows that you are well intentioned) and wait for them to reciprocate. If they don't return your greeting, make a quick retreat. If they bow back you can go closer, and if a Hippogriff accepts your approach they might even allow you to climb on their back and take a ride into the skies.