0- Choose one champion, and focus on him.
1- Practice last hit. There are two major guides for this, scrub's guide and elyndar's guide. I will use the elyndar's guide, but with the spreadsheet from the first one. Do this before every match!!
2- Before the game starts, write somewhere the numbers from abilities of the enemy on your lane (cooldown and damage). This will gradually memorize the timing from your common enemies.
3- During load, think about the early and mid game. How you should play the laning phase?, What kind of mistakes your enemy may do, that you could abuse?, What are the possible outcomes for other lanes, and how each jungle may change that?, What are your win conditions?, what are the win conditions of your enemies?
4- Write in chat the time of important stuff, like summoner spells, and ultimates (You can be even more helpfull, and say when it will be available again)
5- Train your mind. Don't rage. Keep in mind that this is a game, and sometimes you will lose. Don't blame others, don't blame yourself. Sure, you could've played better, but you are on a learning process, on top of that, this is a complex game, isn't just one bad decision that defines who wins.
6- Train your attitude toward others. Treat others with respect. Focus on winning a ribbon. Learning how to deal with people can avoid some loses, and it will be usefull outside the game.
7- After the game, watch the replay, search for your mistakes, try to imagine what you could do better, and look for patterns on the other players (warding spots, where they try to sweep wards, jungle routes, jungle routes and time, ganking routes). Write it somewhere.
Important time on replays, to pay attention: *When you died *When objectives were taken *When many teammates died *Teamfights *Moments that your team's gold advantage was reduced (You can see on the graph on match details).
8- Go on Theorycraft and see if there were better options.
9- Use the lolplanner to plan where you should've warded at each stage, and to make a plan where to ward according to the objective you want to take.
10- Write on a piece of paper what you should focus on doing better on the next match, and keep it next to you.
11- Repeat everything.
12- Outside of the game: Read forums, keep track of patch changes, watch a streamer of your main champion. Suggestions: subreddits of your main champion, http://koreanbuilds.net/, http://br.op.gg/, http://surrenderat20.net/.
13- Keep track of your progress. (The LSI is very usefull for that).