To kill minions only last hit em, u can use the S button to stop your character from attacking this helps, but be careful!

By the time teambattles start if u have 100 minion kills you should be good to go. Aka, if u battle right in the team battle your team should win if everyone does this. This is about 19 min in.

By time game ends you should have over 190 minion kills, more if you didnt participate in team battles. This is about 40 min in. This will show you didnt slack off and its not your fualt u loss, or its your proness that led u to victory.

In team battles try to ignore the tank and kill the one on their team that does most dps. If the game is over 30 minutes in, try to focus on characters like, Yi, Malz, Twitch, Noct, Teemo, Xin, (any range dps), Morgana, Sona, Brand, Annie, Leblanc, Shaco, Ryze(unless he built tank, but if he is fed focus him).
Ramen L: Dont focus on these heroes in team battles, Nidalee, or any tank, Olaf(unless hes fed, if its 50+ minutes, try to keep him exausted or blind him), If morde is going AP focus him. Or u will lose team battle, Focus Kennen always so he cant stun everyone. (Nasus late game pwns everyone at like 50 min in. So you may need to focus him or keep him exausted if hes tanky keep him exausted, if hes dps, focus him.)
Ramen L: Getting Dragon everytime its up will win you a game, do not let the enemy team get dragon, Dragon is 180 gold to your whole team in summoners rift.. If you get dragon its basicly 3 player kills, so in a 50 minute game if u get it everytime its like 20+kills.
Ramen L: Baron is like 5 player kills and a huge buff, so its important to, after 25 min make sure not to let enemy team get it, and if u have a chance, get it!! Its usually auto win if ur not losing. Also its possible to get baron before 25 min. I got it 16 min 30 sec best. U got to have like 2 madreds though.
Ramen L: Letting people get the secon tower in a lane is really bad. U always want it up, that way if u get aced at like 50+ min you wont lose. Never let a tower die if you can save it. It also gives 150 gold to everyone. Also, its worth dieing for a tower. So if 2 of u die for a tower dont worry. 3+ can be negative though.
Ramen L: Tanks should try to build off enemy team, and off whos fed. As cho what you do is aoe everyone then feast the enemys best player. And keep your best alive at same time.
Ramen L: Building tanky, is good no matter who you are.. Any character thats squishy is pretty much useless if the enemies are good, unless you have a really good tank. A malphite, and Shen on same team is usually auto win.