-You can only keep a high winrate if:
1- you're on a win streak
2- you're playing at an elo (typically) below your true skill.
In any other case the system will match you with players that are skilled enough so your win rate is 50%.
Playing as top
-------if bot jungle and mid feed, the chances of winning are slim to none
-----If bot lane feeds, try to not let that feeding affect the rest of your team. In many cases, a feeding bot lane causes jungler and even mid to feed as well. Then everyone gets frustrated and surrenders.
------If mid feeds only, that should not be a big deal if you're playing a tanky top ( I main nasus)
------If jungle feeds, try to not let it affect lanes. Deal with a fed jungler and ward well so he doesnt fck ur lane up as well.
Playing as jungler
------before the game, lolnexus ur game. Try to gank lanes that look like they have a good KDA and seem like they naturally win their lane.
------ gank lanes where the enemy is pushing hard
------ be careful when ganking lanes where there any many enemy minions and enemy has IGNITE. In this case, there is a strong chance the gank will lead to a 1 for 1 trade.
------ I highly discourage ganking lanes that are losing hard, even if ur team flames you and begs for ganks. Ganking losing lanes only snowballs harder.
Playing as mid
----try to kill the enemy mid
----if that doesnt work, waveclear and roam bot (early game)
----if that doesnt work, roam top
----if you cannot get a roaming kill, ward the jungle and roam there
----worst case scenario, farm up mid and pray.