The biggest thing for me is to respect your opponent -- bumping and grinding down low is fine, but don't nail him from behind in the boards, slash him in the ankles or the back of the legs, or bring your stick up in the face area. Everyone has work/school in the morning, and surely many of the guys will have families. Someone shouldn't lose an eye or break a leg playing rec hockey. Shake hands at the end of the game and NEVER carry anything into the dressing room/parking lot area.
One thing I never understood is when people say that so and so player is trying TOO hard. I don't get it...how can one not want to try as hard as they can? How can that be contained? I don't care if you're playing AAA or Tier 7 hockey -- if there are refs involved, scores/stats/standings are being kept, and there is a championship at the end of the season, you should want to win. If others want you to passively play, tell them to go play pick up.