Seriously, how do you know when you're ready? Is there a way to tell by a certain number of classic/TB games won? When you know all counters and know how to play very well on your mains? How do you prepare?
Also, is there a credible website that lists counters to certain champions?
when you don't think you can get better by just playing normal anymore I would say. when normal feel super easy and you continued to practice in normal still for a while. not just laning, but carrying games. that how it was for me at least.
ranked is harder than normals so prepare for that difference (unless you have high normal mmr).
fyi if you have to ask... your not ready
When you understand the game, know the champs and their skills, can play 2-5 champs in 2-5 roles, consistently don't make many mistakes, and can stay relaxed.
You can prepare by playing 3-5 games with each of your champs that you will use for ranked, just so you're familiar, and maybe watching some ranked tutorial/tip videos.
You can just use google and search "LoL counters", there's a few counter websites I believe. They are credible, they are usually based on a user rating system and have tips/comments.
Whenever you have a couple of champs in different lanes that you are comfortable in playing in. It is good to have one or two champs in each role that you know what you are doing. Other than that find a line that you prefer the most (For me that is Support :D) and try to get that lane as much as possible.
P.S. Don't try out champs you don't know how to play in ranked. Even if you counter the other champ, they can still shit on you cuz they know what they are doing where as you don't.
When you have high normal mmr otherwise don't try it cause the system will place (if you have never played Ranked b4) with people around that mmr.
I recommend not going into ranked until you are quite comfortable with two or three champions in each role of the standard meta, so you can fill in your off-roles if need be and know how to help your allies do what they need to do. Practicing these roles will also help you learn how to deal with many champions from outside your favorite lane, so a fed top laner doesn't wreck your game despite your excellent ADC play. A lot of people also suggest waiting until you have at least one rune page worked out, or one page for your main and one or two others for your off-roles. I largely agree with this, but don't put too much weight on rune pages, as intelligent play and a good head for strategy can make up for not having ideal runes (or any at all) until you get to higher levels of play.
I think the best indicator of readiness for ranked play is that you feel comfortable coordinating team strategy or helping other players implement it. Learn and master wave management in and out of lane, keep your death count very low, work with your team to maintain vision control around important objectives, practice setting up split lane pressure before challenging an objective, find out what form of communication lets you work best with your teammates, develop strong map awareness, keep personal presence across the map, and learn how to survive being pitted against a hard counter. Once you usually feel that you pretty well know what is happening in each game and can identify how you could have done better in each game you finish, that should be a good indicator that you should take a look at ranked. If you frequently finish games and don't know why you won or lost, that is an indicator that you are probably not ready for ranked, and should spend some more time learning the game's strategy.
One final note: If you have trouble dealing with toxic players, you should spend some time working on that before you go into ranked queues. Ranked players tend to be a little more stressed out and accusatory than players in normal queues, even if they are usually fine people. Learn to keep a positive attitude, be a friend to allies and opponents alike, and use the mute button when you must.
Good luck and happy farming!
If you're able to fill for any role then you're ready.
