Some ADC assistance........... majorly

OK, so I'm a top lane main guy who also supports, jungles and mids every now and then. The one role, ADC, is one I'm udder garbage at. though i may play squshy mages, i cannot play adc for the life of me and anytime I do i ether feed or dont get much practice at all (mostly feed). Thing is my bro is a support main and i would love to do better as adc so i can play with him and not suck. i would appreaciate if there are any adc mains out there to maybe help the lone top lane main who cant play a marksman for crap. Advice in the comments would help, and i'd be willing to enter normals if you would want to teach me there however i'd appreciate if you are at least knolagable in supports and have the ability to see and stand a bad adc playing in front of your face, making the awful decisions every now and then.

As a bit on who i tend to play as adc, i can play ezreal at least ok (though i still suck as him half the time), I enjoy playing twitch and he feels good to play but i still need to learn him, and any other adc........... well guess.