1- Play what you like and are good at above all else.
Don't worry about counterpicks
Don't worry about whose "OP"
Don't worry about team comp (too much)
If you want to win, play your best champion, regardless of it's meta strength, remember that the meta only applies in full force in high divisions, where everyone is so mechanically skilled at every champ that these matchups become relevant
2- Do NOT point out your team's mistakes
This never helps, but can be a detriment. Remember that you and your teammates don't know each other, thus, when you nicely point out their flaws, your teammates may take it personally. Don't risk that happening, unless the teammate has already shown receptiveness to criticism or is asking for some tips.
NO excuses, you need to buy wards, upgrade trinkets, ward objectives, EVERYONE must do this, yes even you ADC. Wards can net you free kills on invading junglers, poorly called enemy Baron's etc. so...WARD!!!
4- If you win, leave lane
Winning lane is great, but this is a team game. Once you've taken tower, you need to leave lane and go to other lanes to help take objectives, pressure Dragon, pressure towers, take their jungle. Just shove your lane out and go haul your fed booty to another lane to get your team juicy kills/objectives
5- If you lose lane, don't try and win it
Mid and Top, this applies to you 2 in particular. If you die to your enemy laner, even if by a gank, they are now stronger than you. Simply stay back and get what you can. Even if you give up your tower and some farm, that's fine, as long as you don't die again. If your enemy laner goes to help other lanes, warn your team and make the most out of their absence to maybe take tower or farm up. If your enemy is staying but your still able to farm safely, then stay (cos the enemy team will be worse off not having their fed player applying more pressure than you), or, if you really can't lane, go take jungle or go to other lanes to get the rest of the team ahead to carry you.
6- The Objective Order
Prioritise Objectives based on this Order, starting at most important
Don't get greedy for a Dragon contest when you could just hard shove mind and take an Inner.