Be Kind Friendly To Your Opponents - It will help your gameplay
Game Starts:
Jax: "Good Luck, have fun!" Miss Fortune: "Maybe I can finally finish a build on this map. xD" Gragas: "Nah, short game." Ashe: "Yeah we only need 15 minutes to beat you down." Jhin: "gg ez" Gragas: "ready to ff?" etc
Minions have spawned.
The lesson here is just be nice to each other during the game. You really have no idea what you're up against, and you really have no idea what's up beyond your own screen. There's no reason to take the risk of getting cocky, no matter who you think you are, and always play with caution.
That is easily the greatest tip I can give any players for success in this game:
Never assume you know what you're up against, merely because you've achieved something in the game. Always - always - Play with the same caution from level 1 until the nexus falls. Never get cocky, don't assume you've already won because something goes your way. It works in all game modes. Just because things are going well NOW, thing's may not keep going that way. If you toss care to the wind, you will invariably screw up.
Being nice to your opponents is the easiest way to stay cautious. It keeps you thinking about them as equals.