I may not be too great, but here are some important points:
Vision: Even if you aren't a support, learning to ward smartly and often is extremely important.
Roaming: If your lane is doing well and you get a few takedowns, go help a lane that isn't doing very good. If you are losing lane, ask for roams and games.
Wave Control: Always look up your lane matchup before you go into a game. If you have a bad matchup on yoiur end, let the enemy remain near your tower, making ganks easy. If you have a strong matchup on your end, don't feel like your minions have to be at the enemy tower. Using your abilities to waveclear is not a necessity for many situations. Just auto attack to last hit if you don't need to push.
Flexible Builds: Don't just build whatever you usually build in every game. Build things reflexive to the enemy champions. For example, if for some reason you are a tank going against a mage in lane you should build magic resist items suck as Mercury Treads early game. Depending on their team comp, you may have to sell and replace some early game items to fight their team and not just their laner.
Ping Missing In Actions: If you don't see the enemy laner when you should be able to see them, ping missing in action. It could save another laner if your opponent is roaming.
Dodge if they pick Fizz: You won't win.
Be a Role Model: Build a positive atmosphere in chat. A good rule for typing in your team chat is to always act like you're Lux. If they do something good, congratulate them. If they make a mistake, politely give them advice. Whether people recognize it or not, player ability and mood are heavily tied. Happy players will believe more in their teammates, believe more in their own abilities, and not be as saddened whenever they make a mistake.
If you're a high Elo player and I gave some bad advice here on accident, please tell me.