This patch only affects a couple matchups and one item: Night Harvester
I don't personally use Harvester that much, however for those that do, you'll see an increase in ability haste and a lower CD on champions, meaning your first engage power will see a decently good increase in power.

Evelynn is the queen of fear tactics if you can't predict where she's going to end up. Being able to go where she pleases without anyone knowing where she is without control wards, this is what makes her fearsome in the eyes of anyone who might see her being picked in the lobby.

Evelynn has insanely good scaling for the game and one of the best AP bursting in the game once she gets to the mid-late game. With an insanely good stealth reliant mechanic, Squishies stand no chance against her once she's started to get her groove going and it makes your enemies play more cautious if they're afraid of you. That may sound like a bad thing, but you never know what they'll do if your team plays aggressively and they're wondering if you're nearby again or off in the distance somewhere else.

Evelynns playstyle is meant to get into the enemy teams line of defense, assassinate a target quickly, and get out before she gets in any real danger. You normally want to avoid ganking before level 6 unless you have a laner who can set up and help you hold someone still for a kill like pantheon, swain, veigar, etc. or if the enemy is very low and you're already nearby and confident the enemy jungler isn't waiting to just camp you out.
It's in your best interest to hit 6 as soon as possible since you have no real pressure or gank threat before level 6 since you can't fight many junglers head on before then, and then use your power spike to get into lanes who you know are gonna be able to assist you or who have heavy CC so that you can get either a kill or have the enemy use up their spells early for a re-gank not too long after if you can't secure the kill.
It isn't your job to only help your laners get ahead, but get yourself ahead as well so that you can start becoming indepdentent in your damage and be able to handle situations if your team isn't around.

Once the mid-game hits is where you really shine. It'll be your job to access the backline and get rid of the squishy damage dealers since you're technically an engage. If you're successful at getting rid of a squishy carry like Vayne, Jhin, etc. then you basically set up your team for a good engage. Mid game for you will be all about getting yourself fed more and getting objectives as best as possible and stop splitpushers if you've got the power to do so.

Late game is your heaviest powerspike. Only tanks can really stand up to your one shot potential. Anyone who is squishy will not survive you as long as they can't react to you in time. It'll be your job late game to make sure you can stop sideline pushes, get objectives set up and be the one who gets rid of 1-2 enemies before the team fight even starts.

Remember: YOU are in charge of setting up a teamfight by getting rid of the enemy carry before the fight really begins.

When the game starts, I usually prefer to start blue buff as it feels quicker to me to start there, kill gromp with smite with level 2 W, take out the wolves and then you can either take out red buff or raptors before heading to scuttle. Just be mindful you might get into a small trade with the enemy jungler depending what side they started on.

The fastest way to get scuttle isn't to full W it. You want to smite it, Q and empowered E combo it as that will nearly insta-kill the scuttle and give you enough time to escape before the enemy jungler shows up and get you closer to your frozen smite.

Once you've gotten scuttle, you can try to go for the other scuttle if you feel the enemy jungler isn't there yet, or you can get your raptors/red buff, go to krugs, then go back up to kill wolves and/or gromp while checking your lanes to see if anyones pushed in by the enemy team before deciding to back for your first item.

You'll normally want to at least try to put pressure onto an enemy laner if they stay with low health as that'll force them to either run and lose CS, use a summoner spell like flash to escape, or die and give you early gold and a dark harvest stack. Most of the time they'll flash away if they have no mobility to escape once you W them and you're too close.

Afterwards this will mostly be you trying to help your laners based on who has better CC, who needs the help and who's going to be able to peel for you in the event something backfires or the enemy is going to try to run before hand. You don't wanna help a lane that you know can't or won't help you, but that doesn't mean leave them for dead, you may just have to leave them to dry longer than the other lanes.

-Impressive Scaling Power: Evelynns scaling is one of the best in the game. Her power does not ever go down and in fact gets more fearsome to fight as the game goes on, meaning you can't ever expect her damage to die down unless she's behind

-Great Ganking: You can't always see Evelynn coming, so you could be minding your business, suddenly you hear the kiss, see the icon and realize "Oh god she's here" in a heartbeat. It's hard to notice her coming and it's even harder to escape her if she full charms you while your laner is attacking while you're being CC'ed by her and bursted down.

-Great backline access: Evelynn makes for one insanely good carry against squishy teams if she's good enough. Alot of the time she can engage in the backline, and take out 1, possibly if lucky, 2 enemies and get out before she's in any real danger as long as there isn't a control ward watching her path behind them.

-One Shot Potential: Evelynns one shotting is insane mid-late game, as it's hard to stop her once she gets ahold of you. She won't need to rely on her charm once she hits her 3rd item not including boots, sometimes her second item in fact.

-Fits into most team comps: Unless your team is full of ranged champions with no frontline, Evelynns got a place in most team comps being able to be one of the main damage sources for her team. She's a solid ipck if you know what you're doing and if your teams comp is good enough to back her up.

-Very Weak Early Game: Evelynn lacks any real ganking or damage potential in the early stages of the game. That isn't to say she can't gank pre-6 if her laner has gotten their enemy laner low enough, but it's still a risky decision regardless.

-Easily Spotted: Evelynns stealth can only get her so far. Control wards which are heavily bought, easily prevent her from getting good ganks or roaming off if they're not cleared or if they're bought too frequently.

-Horrible in prolonged fights: Evelynn is meant to get in, get a kill, get out. Staying in fights longer than she has to is not her speciality. If she can't get in and kill someone, unless she's got team members nearby, she'll more than likely die without some kind of peel.

-Insanely Squishy: Evelynns charm does give her peel to counter this, but if she's caught out she can easily be removed in seconds. You gotta be prepared to get one shot while also doing one shots yourself with her.

Dark Harvest is personally my favorite rune for Evelynn. It not only helps her scale even more than she can now throughout the game, but also helps burst down enemies faster resulting in even greater one shot potential.

Sudden impact is definitely better than the alternative. While cheap shot can be an option, you normally stop using her charm as often later in the game and sudden impact scales better. Sudden Impact provides you with better magic pen as your E triggers it and causes you to do extra damage with your empowered E.

Again, Eyeball collection is the prime example of being the better alternative of the other two choices as it helps you gain more AP as time goes on in the game, still adding onto your damage power.

Ultimate Hunter for me at least, is a better choice. It gives you faster access to your ult in the longrun, giving you 25% ult CD reduction once you have all the stacks on an enemy team meaning your ult will be up practically every fight to use for execution and/or escape.

Absolute focus is definitely a thriving choice on Evelynn. Your job as her is to get in, get a kill and get out meaning that this will help you do just that as long as you stay above 70% health. Since you have no need for extended fights, this is definitely your choice for more burst power.

Gathering Storm is great for Evelynn since she has to scale for mid-late game anyways, and this helps her do just that. By the time the 20 minute marker hits, it's almost if not already going to be mid-game, so you'll have 24 extra AP that will keep increasing as the game goes on. The longer the game, the harder you scale.

ALTERNATIVE CHOICES
Electrocute is the meta choice seeing as how it scales off AP and Level, while that is helpful, as I said I prefer Dark harvest as I'm playing for the late game anyways and feel it does better. Electrocute however is defintely a good alternative if you don't feel like you're capable of getting souls to scale with.

Relentless hunter is another heavily used Evelynn rune making her capable of chasing, gap closing and running away as needed. It's overall good for just keeping the pace of chaisng someone in your favor.

This is mostly chosen due to the fact that it helps cost effectiveness of having to buy regular boots over these as these give a bit better movement speed overall. It makes roaming and chasing/fleeing much easier.

Cosmic Insight is used for giving your spells and items shorter cooldowns in the longrun. It doesn't scale up however, so I don't personally see much use for it like others might but since you're using rocketbelt and possibly Zhonyas, it works to have those up faster.

Evelynns passive, Demon Shade will put her in a shroud of Demon Shade after 4 seconds of not using abilities or being in combat. This can restore 15-75 health per second while below 259+590 health +250% AP scaling, and grants camoflauge from level 6 and forward. Taking tower or champion damage removes her passive for 1.5 seconds. This is her main way of travelling without being spotted and what makes her ganks so dependable without being seen. Not only that by the time you build rabadons late game, you're healing back to full health once you're out of combat.
Evelynns Q is Hate Spike and is her most used ability. It causes her lasher to strike out and deal 25-45 damage based off level +30% of AP from the first enemy hit and then does 10-50 damage +25% AP scaling damage. She can recast this 3 times with spikes that will attack the target marked with her first Q or the closest enemies with 25-45 based off level magic damage +30% AP. Her wave clear is insanely good due to this ability.
Evelynns W Allure will curse a target champion for 5 seconds which will slow a marked target for 0.75 seconds, refund the mana cost and remove the mark. If the mark can last 2.5 seconds, its full duration, it can charm the enemies hit by her next attack for several seconds and removes 25-35% based on level MR for 4 seconds. You'll tend to use this alot early game for the charm/slow and to get extra damage off for your burst combo. I prefer to get this second in case I get early invaded, but level it last
Evelynns E, Whiplash will have Evelynn whip an enemy dealing 55-115 +AP Scaled per 100 AP of the targets max health as magic damage. She also gains 30% movement speed for 2 seconds. Entering demon shade resets the cooldown and empowers it causing her to instead dash to her targets and deal 75-175 +4% AP +2.5% per 100 AP of the targets max health as magic damage including to whoever she passes through. This will give you your final major burst of damage excluding your ult when engaging someone. A good early combo will always end up being W into Q+Empowered E then Q spikes followed by an ult execute if they are about to escape.
Evelynns Ultimate Ability, Last Caress will unleash her demonic energy to deal heavy damage and cause her to teleport backwards while being untargettable dealing 125-375 +75% AP damage. If enemies are below 30% health, this damage increases to 300-900 +180% of AP magic damage. The extra damage will be indicated by a marker over an enemy that shows they will take the extra damage but doesn't mean they'll die, just take insanely heavier damage. Use this to escape, gap close or execute as needed as it has more use than just for damage.

Evelynn can be an easy champion to use at times, but hard to fully master. Hopefully this gives you better insight into playing Evelynn if you have zero clue how to play her in the first place and maybe you can improve off of what I've said.