Some general tips
-Last hitting is ultra important. 15 minions is a kill essentially i believe. Takes priority over poking or doing occasional damage to enemies. Unless you are sure you can get a kill or force them to back and give you free farm for a bit (or at least prevent them from farming consistantly) make sure to focus on your own last hitting first.
-DONT overextend. Pushing a lane to hard is very dangerous. Unless you know where the entire other team is (mid and jungle if your top and bottom) be extremely wary overpushing, as your prone to getting ganked. Which leads to the next tip
-WARDS. Never ever underestimate warding. Its everyones job. If you have a free slot, and some extra gold, get at least one. Trinkets alove simply isnt enough. You m ay think our saving for that next item, but the measley amount a ward or two costs is insignificant vs the significance of being aware and preventing bad situations. I mean seriously, they are 75 for a green and 100 for a pink. Chump change.
-Always keep moving. You shouldnt ever be just standing there taking shots, or even waiting at tower for creep wave to arrive. Avoid the easy target for skillshots and poke, keep your enemy guessing. Predictability leads to traps.
-AS ADC know all the adc's. At least read up on them and know their skills, their ranges, you can google their playstyles, w/e. Just be aware of how your opponents champ works, so you understand when they might be about to go all in, when its to dangerous to jump them, when they are weakest. Safe spots from their skills. Knowing your enemy is very important. On that note know how enemy supports work as well, since they are an equal part of bot lane dynamics.
-MAP awareness.always be paying attention to the map. You may see a gank incoming, you may see someone in trouble in your jungle, you may se a nearby lane that needs some help or saving. Being aware of whats going on is a huge help to your entire team and the future of your team.
-COMMUNICATION. Keep in contact with your team, notify mia's, when your low on mana, when you plan on going for an objective, ect. If everyone knows what everyone else is doing/seeing, you work much better as a team.
-ATTITUDE. Staying positive is always key, above all really. Its a game, have fun. Have an asshole teamate? Mute him. Right away. Dont waste time and frustration arguing. Save yourself the distraction. Dont get worked up over bad teamates. It happens. Try to be friendly and help them with suggestions, but dont be a dick about it, that helps no one, pisses people off, and mad/stressed people play worse. If your losing, try to turn it around. Try to learn a strategy to deal with what the enemy has, use it as an oppertunity to get better. Getting mad at it wont help you grow from the experience. Is a game at the end of the day, so have fun. If an enemy ganks you hard, congratulate them on catching you off guard, and learn from it next time.
I dunno, so much more, tired of typing XD
There are tons of youtube videos and articles online from people who really have everything down to a science, spend some time doing homework.
Look upp strategies. Look up builds. Dont have to use only a build someone else has, but you can see what they did, learn why, and gain some understanding about a champ from how they built him,/her, get a better idea how a champ functions Worth doing even on champs you dont own/play, just to know the competition.