First time ride advice Doing 75 km "Ride For Heart" in Toronto this Sunday on a closed highway. 
Using Norco Cyclocross bike for it. 
I've read online different advice for beginners, but was wondering if there is anything else the community can suggest. 


Be polite and communicate intent with other riders 
Cadence ~ 70-80 rpm
Drink/Eat a bit throughout the race not to reach the state of bonking and dehydration 
Have fun :) 


Am I missing anything important? 



Update:
Thank you all for the advice. The ride went well and we finished in about 3.5 - 4 hours.  Avg Speed was ~20 km/h. Highest recorded - 37.5 km/h :) 
I don't know how to pick the "approved" response because many people contributed very helpful info.
With respect to riding in a group, or with more numerous riders closer to you than you are used to.


Be aware of the space around you
Maintain a safe distance from riders in front
Look sideways and over your shoulders before overtaking or maneuvering
When cornering be aware of riders to you sides and give them space
When slowing down, hold up a hand palm forward, or call out 'slowing' or 'stopping'


Common sense stuff really.