Originally Posted by Nocturnes
Pick one or two champions and pick one role and play only those champions in only that role. This way you can focus solely on working towards your elo goal without having to diversify and deal with multiple champion types and situations.
Terrible advice because it's only partially complete advice.
Learn to play one specific role very well, but know how to play one other role and support proficiently. If you do not know how to play support, don't ranked until you learn how.
Take me for example. I main top and that's my absolute preferred lane and I like to consider myself as pretty good in that lane. However, I also know how to play mid and support proficiently.
So long as you know how to play three roles with one of those roles being support, you'll do fine. I got to diamond last season only knowing top/mid/support after all :P