As far as roles are concerned, ADC is a lot different from the other roles in terms of champion pools. Most ADC's don't actually fit too well in the other lanes, and meta picks for the other roles don't normally mesh well in the bot lane as an ADC.
As far as ADC's are concerned, I don't play it too often, so I can't really say too much about ADC's to learn. One thing I do think has value for the ADC role is learning some of the caster-based ADC's in the bot lane, as learning one or two caster-carries like Corki, Ezreal, or Lucian really helps learning some of the other roles. Corki is personally my go-to ADC when I have to fill for it, and I personally think he is really good for both mid laners to learn to play ADC's and for ADC's to learn to play mid laners because he casts spells and auto attacks so much.
I would recommend that your next role be support because you likely already have a good understanding of what to do in a duo lane. You already play one half of the bot lane, why not play the other half? I can't really recommend too many supports because I also don't play support a lot. You probably have quite a bit of experience already playing ADC, considering it's your predominant role, so chances are you have already played with and against quite a bit of supports. I would recommend you try learning a support based on what you think you would want to play as a support and what the supports you have played as or against have done.
On a final note, something I feel sounds strange at first but I think has some real merit is to learn how to play your favorite champion in some of the other roles. Jungling with Jinx isn't ideal, so don't try that, but try taking a solo lane with her. You'll get into some unfamiliar lane matchups that you won't otherwise play, but because you see these weird lane matchups you will improve yourself by making you able to better adapt your play to what your opponents are pulling out. In addition, you also get to learn the other lanes in a more familiar environment. For a while I was playing Trundle and Shyvanna jungle, and I didn't know how to play top lane well, so I started playing both of them in the top lane instead of the jungle. I got better at both champions by learning how to lane with them and I learned how to play in the top lane better.