Kayle Tips

To get right into it: Kayle is an auto focused champion so she has many similarities to the general gameplay, dodging skills and slashing from an apropriate position.
But I hate playing adcs, Kayle has some important diferences.
First is that Kayle has an ability to basically fully counter most asssasins without using flash and heal, even with that stay close to your team, you *might* not be able to solo kill that 11/0 Rengar (this is sarcasm, you won't be able to without flash, unless you're also 7/0).
Second is that you're a solo laner, mid laner in my case. The major diference of going mid rather than top is the Poke and Roaming you will be forced to deal with. This is might be wrong but as a midlane it's easier to play safe without the midlane and jungle coming to dive you bot lane.

I played Kayle in the Top lane in S6 and S7 the main diferences you are going to have are:

-Trading is bad for Kayle in most matchups, midlaners usualy have a small burst they can employ but kayle has the opposite: a ramp in the damage. You fair better if trades take enough time for you to auto attack the opponent but not enough for their cooldowns to reset. Since my rune of choice is Lethal Tempo the ramp is even more steep. I played quite a bit with the other runes but lethal tempo is definitely the one I felt best with, it helps a lot to make you threat right after finishing Nashor's, without it you would be gated until you dual wield your rageblade. You can also have a pressure in lane by triggering it with your E splash from a safe distance. While trades are maybe worse for you in mid the consolation prize is the small sustain you have from W, mostly because of it I start itens from the AP parts so the heal is more mana efficient. Don't spam W too much or you'll run out of mana, try to wait for the manaflow band to use it if you're able.

-Roaming is bad for you mostly because you want to dual wield as fast as possible, the spike in damage is pretty substantial, so you want to afk farm. But alas, you are a mid laner and risking a gank in the other lanes might be worth it if you can get your team a kill or avoid one. Before Nashor you are really weak and you are especially lackluster before you have your Ult in your hand, but if you do have it, it can be used quite effectively in skirmishes in the bot lane. If you were Top You would need to use TP to help bot lane anyways, but you have an extra summoner to safely get through the laning phase, and sometimes you can force midlane to stay by pushing or following close to them. It's quite sad to waste TP as a top lane Kayle before Lv 6 or Nashor, you really are there mostly for moral support, you are an angel after all, you define morality.

+Gank safe. Kayle doesn't have a top tier escape, so being mid lane rather than top is really a breath of fresh air, junglers will have a harder time ganking you.

+Burst negation, in the other side of the coin from the down sides of trading is the potential negation you have from your ultimate. Mid laners usually have small bursts of damage they dish out or a burst ultimate you can negate with R. Be very aware of CCs, if you hold onto your Ult too much you might get slaughtered and (?) pings will ensue.

Playing well: no matter witch champion you are playing, game knowledge and decision making are your best weapons. Maining a champion will give you that more of an edge, making you comfortable and used to playing a certain way, but it is only an edge, try as much as you can to minimise your decision making mistakes.

Tilting: If you are really stuggling, your team is making bad decisions constantly, well you at least know where your Wit's End is, either in the shop or your hand.
Jokes aside be aware that if you start to play badly just because your team is 0/6 fixing this should be a first order priority to playing scaling champions like Kayle. Comebacks are likely but don't expect them to not get yourself down if your team doesn't manage them. Play safe, truly, don't put yourself in danger if your teammate invaded and you know the enemy team surrounded him, unless he has high mobility your ultimate probably won't be enough to save them.
Sometimes you will die before ulting, maybe by your mistake, maybe because you were bursted with cc and you didn't predict it (maybe they flashed). Your team might complain in the first case if they are paying attention, or already tilted, and you have to deal with it. Don't feel too bad about these mistakes because feeling bad is detrimental to your concentration, but be very concious of them and always try to improve, think back to it and figure out when would have been the best timing to ult. Everyone makes mistakes, sometimes concentration will escape you, just make it a learning experience as much as you can.

Ultimate
Sometimes you will need a good timing, ulting on picked off allies who have skills flying towards them, try to ult as late as possible before the skills hit and only if it's a significant amount of damage (and he is not already basically doomed, no escape + in the middle of the enemy team + your team is not close enough to save him). Sometimes you will need a good reaction time, ulting when eve will attack you and proc charm, when rengar jumps on the backline, or someone flashes to cc. (malzahar, bruisers like jax, riven, irelia, camille).
You not only have to be aware of these plays when they target you, but also the adc and sometimes other roles to prevent the faceroll of your team. The problem is that saving someone is also not always the best play, maybe saving ult for the adc and you might be better.
One of the best uses is when a squishy is caught by the enemy team and they use a lot of important skills, if you are able to negate enough (if they use enough skills) you are able to completely turn the teamfight if you favor. Of course your team needs to be close, like in a cenario the adc gets hooked. Sometimes it's a gamble, you might not be able to react and use your Ult only if they use skills, and they might not use almost any at all, and then you basically wasted it and an assassin just jumps on you.