Don't limit yourself to one role right at the start. As a new player, you really want to familiarize yourself with champions. You won't see what an Ahri or Darius is capable of if all you do is play bot lane ADC. I wouldn't want you to think that just because you won your lane, you can chase that Dr. Mundo through their jungle for a free kill.
Once you have a general idea of what all of the champions can do, you should learn to watch for them. Warding is very important. Even as an ADC, you can find a moment when you're level 9+ to spend 250g to upgrade your trinket; it won't set you as far back as a lot of people would have you believe.
Unfortunately, placing wards just isn't enough. While you're CSing and dodging evil Blitzcrank hooks or Ahri balls, you need to glance at the Minimap to watch for enemies coming to your lane OR opportunities. Sometimes the enemy players just overextend from the rest of their team, and you are close enough to take advantage of their mistake. The ability to determine the difference between when they are over-extended enough to safely kill is a good trait to have.
So. You have a good idea of what all champions are capable of (Are they doing mostly physical, magic or true damage?), you're placing a couple wards, CSing, keeping safe from hooks, and often glancing at the mini-map to keep track of where enemies are. At this point, I would definitely say you're ready for ranked play.
I wish I could tell you how to climb to the highest tiers of ranked play, but I'm not quite there myself.
P.S. You won't learn all of this overnight. It is going to take months of practice, and you're going to run into a plethora of abusive players. Do your best to ignore their verbal assaults, and don't respond to them with negativity yourself (You may their comments to be very difficult to shrug off after a while; at least I did.)