I'm pretty much just noting these down to share with some friends. I'll be editing it frequently, so come back and check it out if you are interested.

1) Soundcheck / Videocheck before the game. Not that many of your loyal fans mind a brief pause, but it will keep everything running smoothly and you'll appear more professional on air.

2) Avoid Tunnel Vision on one lane or character. Often your focus will be on bottom lane because there are more champions down there. Don't let this happen. Your viewers would much rather see the solo lanes and ganks going down instead of watching and listening to the usual lane-exchange happening at bottom.

3) Flip Through the Spectator Tabs every 30 seconds if possible. Even if a particular stat / piece of information isn't important at the moment, you never know what the viewer wants to see. When you are trying to please everyone, do it ;)

4) Involve the viewers whenever you can. This includes asking/answering questions whenever doing so will not distract from the game. Two great examples of this would be Guardsman Bob, and the Smite Club guys.

5) Stay Objective. It is so easy to get pulled into the excitement of the game. Even more than the players, the commentator should have his eyes on that mini map. Make it a point not to miss top and mid skirmishes. Whenever there is a lull in play, flip through the map awareness options to give everyone a from-the-team point of view.

6) I'll add more later. If you're commentating on games, you're already doing your part to contribute to the LoL community, and we both thank and love you for it!