Fields vary. For instance my rules at LZ Woodstock vary from Joes at Flagraiders, Wolfpack's at Muskoka etc. Find the medium that is best for your team. The obvious rules like eye protection, even if it's just certified safety glasses, bolles whatever. 425fps is generally the highest AEG limit, exception is for snipers who need backups etc. And as Phalanix said it's always good to have a mercy rule in effect too. Never sacrifice safety and don't be afraid to talk to those who blantantly ignore or risk the safety of others.
"Tu Fui Ego Eris"