Hi there,
what "things" do you wish you knew before you started running a relay?
I wish I knew what the tor community and the tor network expects from us. For example, is it expected from us to keep the relay with 100% uptime? or would it be still fine to -say- have 70% uptime? or if it is not > 90% uptime, is it worthless to run it anyway? Or, more general, how much time and effort does it take to set it up and how much time and effort does it take to keep it running? What minimum knowledge do we need? What is the minimum requirement the relay must have to be it worth for the network?
Also, I wish I knew what are the possible problems we may have to face and what to do with them (example, run out of bandwidth quota, cpu usage, possible intrusion and attack vectors to the server running the relay and how to prevent and mitigate them, ...)
Sometimes I find those answers on tor's page/wiki or ask them on #tor-relay. Perhaps I didn't do enough research before setting up the relay....