Go to the "Game Info" tab at the top. Then, click "Champions". Then, click each of the listed champions to learn incredible specifics so you learn half of what it takes to counter them.
Assuming you've done that, now play each of the champions yourself. Take note of when you get caught out and are completely useless. Use these notes to figure out when its a good time to engage them when you're on the flip side of the coin.
Personal notes: if zed ults you, dont flash or dash until he respawns. Most Zeds will shoot their shadow behind them to dash back to it and let his dmg double on you while he's far behind the tankline, so its unlikely he'll chase you very far. I said UNLIKELY. RIP Zed ult. For Shaco and Teemo, don't bother them 1v1. They aren't shit if they don't get kills and they're a migraine to chase, so just don't. Leave them alone entirely (unless you have TWO other teammates) and they wont be a problem at all. Yasuo swirls when his tornado is ready, so gtfo and wait for him to use it, THEN go in. I've got more, but I don't wanna type it all. Let me know if you want more hints, or anyone add to this if you feel like it.
GG.
P.S. I have no notes for Vladimir. Want a note? Ban him. It's what I do. :P