How can i run my fastest in an 800 metre running event?

This Friday is Athletics Day and I will be competing in the 800 metre running event. How can possibly run my fastest. Is specific thing i should do before the race (e.g. breakfast or no breakfast, or have sports drinks or water). And also because I'm only in grade 6 no one actually does the on your marks get set go. Everyone just stands and does not start off on their knees. What do you recommend i Do?