Pre-game
Wasn't sure where to post this suggestion.
To paint a picture, in the pre-game interface where players choose their champions. My suggestion is to add a reminder, a sound or a pop-up, which will remind players to pick their champion before the timer runs out. This reminder would only be received by those players who have not yet picked a champion.
Too many times have I been kicked for accidentally not choosing a champion, and too many times have games been canceled due to someone not choosing their champion. This suggestion would help minimize the stress experienced by LoL players.