A practical, but very good tip from Shyla.

Always turn your camera OFF before your switch your lenses. You are probably thinking to yourself "Duh Shyla!" ...but for some reason it never occurred to me that when my camera is ON, the sensor is magnetiezed and attracts dirt! I think I slept through lens changing 101! It's hilarious when I shoot agains a blue sky and start thinking..."it's a bird...no it's a plane...no no it's dirt on my sensor!"  :0)

Thanks again Shyla for all your great info!