I do it in a very simple way, making sure my lips don't even touch water.
I shower with 2 different positions in 1 go:
-Standing up straight, shower head just below my chin. Wash your body below your head: neck and below.
-Leaning over, head down, your face looking in the direction between your legs (or in front of your legs, make sure that the top of head is directed as much down (vertical) as possible. Shower head held in hand: and carefully aim the shower beam towards the sides of your head and shower from the back of your head slightly forward, making sure the water beam doesn't touch your face, while washing your hair. It looks like this:
PS. Sorry for my poor drawing skills! :P
PS 2: I wash my face gently during shaving, applying wet hands on my face around my lips.