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tell me whats the best mid champions to carry silver and bronze ?
I would say atm u can play ekko/wukong/kassa in lower elo. They are all pretty simple to play and have good scaling which is important for long games. Also the winrates of the mains on those champs are the highest on average.
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How to teach yourself a better ADC positioning?
First u need blue trinket so u can ward things without having to actually run there. Then it depends if u have a dash or not or if u have flash up. Lets say u dont have a dash like ashe and u dont have flash atm. Then u can see who is missing of the enemy team and where that champ could possibly come from. Some champs cant go over walls etc. If ur team is not defending u and u cant get close to them anymore u can also wait until the wukong goes in on some1 else until u start to deal dmg. Instead of gambling and hoping hes not there. Usually u want to stay behind ur tank and near ur support so even if they dont actively follow u then u just do it urself. Its always a good idea to stay way from brushes. Basically position urself as far away from anything where u dont have vision on.
U can always watch ur own replays to see where u couldve stood and watching high elo replays of people playing ur champs helps aswell. U can see where they normally stand while pushing or sieging etc.
Next thing u can do is if the enemy team doesnt have tanks u dont need pure dps items and can go ga/pd/etc instead of a third pure dmg item. That way u dont get insta oneshot by one ability. Then ur positioning can be a bit worse and u dont instantly lose the game. Also keep in mind that its ok to die sometimes if the enemy team had to use alot on u. So if they want to use 3 ults and their flashes etc on u thats fine ur team will probably win the teamfight then. Try to stay away from ur mid laner usually aswell because if they get u both with their aoe then ur team has no dmg anymore.
Overall i would just play the same adc as much as possible so u learn from ur teamfight deaths by playing alot +replays + replays of high elo mains.