What is the best way I can ues my 300mm?

I have a Canon Rebel SX with a 55mm and a 300mm. I ALWAYS use my 55mm but not so much my 300. I've been getting really comfortable with my 55 and feel like I'm ready for my 300. I wanted to know the best ways I can use it to get the most out of it, don't want to use it just like a point and shoot. If you could tell me some good tips that would be very helpful! :)