So i decided it's time to master the art of animation cancel to improve my damage output. I want to master this mostly to main 
for ranked matches. Any tips or advice that can be usefull will be highly appreciated! Even vids!
It's not as complicated as it sounds. Watch/listen to your champion, when the damage applies issue another command immediately. Most of it is down to practice as eventually you can get the timing into your muscle memory allowing you to perform the animation cancelling instantly instead of reactively.
Animation cancelling won't get you out of low Elo though, just focus on learning the basics of the game at this stage. Getting good at animation cancelling is only relevant when you get to high Elo (above the people who don't know the basics of the game).
It's a great thing to learn, however if you're looking to progress in ranked this isn't your ideal start point. As was said, it's something you pick up over time and will be reactive at some point but there are much more fundamental parts of the game you should master long before animation canceling.
For example, do you understand how to treat every possible lane with Riven? Do you understand where her powerspikes come vs other lanes you're likely to face as counterpicks? Are you an effective proxy farmer? Do you understand acceptable gains and losses? When to splitpush? When you want to force a team fight and siege a lane? When is ideal to ward where?
All the little things like that add up.
Your E can pretty much cancel any animation. Your third cast of Broken Wings can be used to cancel you're Windslash animation.
