Learning atleast 1 champ for every role will come a long way..
Too many times I come across ppl in ranked who cant play ''X'' role and a high number of these ppl go on to complain about it nonestop in game and usually feed. I mean you dont need to have a massive champ pool some ppl climb playing only 1 champ... All I am saying is if you really cannot play a certain role and Q up for ranked then you should accept that you might get stuck playing it at some point. Why set yourself up to fail when you could be playing a few normals or bot games to master atleast 1 champ in the role you feel you are weak in.
My midlane sucks balls and whenever I would get stuck playing it I would let my teammates down constantly and I decided to take a break from ranked matches until I felt I could hold my own with atleast 1 mage. I played like 20 games of viktor nonestop in normals and finally felt comfortable playing mid in ranked since I have him in my back pocket now and have also picked up leblanc recently just incase i need a more mobile mid.
Now that I can hold my own in every position I usually give up my role to someone if they want it but I cant say the same for others. Its probably a lot easier to just learn the damn role you suck in.