My advice is "give leagues a nice health break". While things have been changing the pre-season hasn't really seemed to be all that much stranger than last season to me once I got past the initial understanding all the new changes. So it's very likely you just need a little break to clear your head and come back stronger.
It's an assassin's job to assassinate adcs regardless of what's in their way, Tanks aren't supposed to die very easily, and adcs have to kite it all out like crazy. It's a hard life keeping the positioning right at all times. I recommend using attack move (A - left click) which will help you easily move and then auto without worrying about accidentally clicking on the ground instead of the enemy and walking instead of auto-ing. The other half to this is always move inbetween auto-attacks. There's a window where you can't attack again anyways so take that time to move, this is crucial for your positioning and will save you from getting easily taken out. Especially if you have red buff or furor (or both) then this can allow you to kite around enemies all day. Remember that as an adc positioning is crucial and it's all about continuing to auto-attack throughout the entire fight. Don't worry about getting their most important targets. Attack the nearest enemy and keep out of the range of the farthest forward opponent so nobody can kill you.
Leaguecraft 101 is a great youtube series and even his older videos are still very relevant since the theory behind LoL hasn't really changed, just some surface things. I found those really interesting and it's what made me more confident as a player.
Don't expect to always get it right. Just keep focusing on how you could have played better and accept the challenge of facing a tough opponent. League would be boring if you could just win every time. Don't worry too much about grinding out wins, think more about how you can get better and enjoy the game more.
