So you decided to pick up Lillia top.
Welcome to one of the most fun champions to date in LOL.
When you look at Lillia you see a Jungler but she does very well for herself on the Top lane even after her tank build with Jack'sho was nerf.
I as a player that has been playing Lillia top pre Jack'so build will try and do my best in helping you understand this lane.

First and foremoust wave knowledge is important.
Lillia has a bit of an issue though. Because her bread and butter, her Q, is an AOE abillity, you will end up pushing the wave as you are harassing the enemy. So keep that in mind as you are farming. Especially if you want to play the lane as safe as possible and you opt for the poke build in which you just sit behind, farm with Q and spam your E in the wave when the enemy is either coming in to take a minion or in the auto-attacking animation.

Remember your mana is limited. Buying Corrupting Pots or using Mana Flow Band makes the lanning more acceptable. You can spam your abillities when you buy pots but remember once you're out of mana you are effectively useless.

Going back to waves of minions. You wanna try and keep your Q Passive stacks up. As you know Lillia's gotten 2 passives. Her Q passive gives her increased movement speed per each stack that is given to you when you land any abillity including your R. This movement speed is also further increased by your AP (3% movement speed per 100 AP). Maintaining this movement speed is what makes Lillia soo fun to play. In fact it's what makes people hate playing against Lillia. Especially if the player knows how to move. Will it take you timea to get used to spacing and kiting with all of this movement speed? Yes, but once you do she will become your favorite champion.

There's not much else to add here as it depends a lot on match-ups. We all know that Top lane is the most match-up heavy position. You will have to play a lot of games against a lot of different champions to fully grasp Lillia's strengths and weaknesses.

When it comes to runes Lillia is quite versatile.
You can run a full damage page with Dark Harvest and AP scalling.
You can run a poke focused page with either Summon Aery or Arcane Comet with some burn and mana sustain.
You can run a sustain page with Conqueror to use against bruisers and tanks a like.
You can even try having fun with some Grasp of the Undying shenanigans with demolish and just split push all game.
Of course rune optimization is first of all a preference I'd say. You can run any of these pages into virtually any match-up but some are stronger than others in for example range match-ups.

Items
When it comes to items there is not better item than Liandry's Torment. It perfectly synergizes with Lillia's burning passive. It also gives you the mana sustain you lack. Other items that work perfectly with Lillia are Cosmic Drive, Demonic Embrace, Rylai's Crystal Scepter, Dead Man's Plate, Force of Nature. Of course there's room for change depending on what you're fighting or how you wanna play. You can opt for some more close quarter combat with roughly the same damage but a that bit tankier by going Rod of Ages with Seraph's Embrace. You can try going Luden's and buying other magic penetration items to instantly destroy the enemy adc. Maybe you want a tankier version with something like Radiant's Virtuer/Jack'Sho/Iceborn Gauntlet/Heartsteel in combination with Demonic makes you take virtually 0 damage less they build stuff to counter you specifically.
You may look at the itemo choices and see that I decided not to put Demonic Embrace in a lot of builds or Zhonya's Hourglass. The reason is purely playstyle. I prefer to do my damage in one abillity rather than burning them. Yes I go the burn route with both Liandry's and Demonic in games with a lot of bruisers/tanks. Yes I recommend Liandry's into pretty much anything but because it gives you abillity haste, burn that is great against any type of champion and mana sustain. Zhonya on the other hand I think is only acceptable when they have a lot of big aoe/point and click stuns or hooks. Lillia thrives on moving fast and not stoping. Using Zhonya is counterintuitive. You start losing stacks and the only reason you'd get Zhonya is to flash/jump into the entire enemy team, press R and then Zhonya. Personally I think you should get used to fighting into 3+ enemies at once so you don't ever feel the need for Zhonya. A properly landed E can give enough value by ulting 2 people than ulting 3 people that are irrelevant and you end up possibly dying because you'll be stuck in stasis.

In the end I want you to experiment with your own runes and items. If anyone tries AD Lillia come and tell me how it went it may even be an ok off-meta build if you need AD who knows.

Now if you're wondering why I chose to run ghost instead of flash it is simple. Speed. Speed is the name of the game when playing this lovable deer.
Why exhaust? Because it gives 35% damage reduction and slows them down enough for you to either catch up or run away.
Why do I chose not to run Flash? Because I feel comfortable to play without the need of flash. I enjoy running around the enemy even at dangerously low HP and just kite around them. I prefer to have fun over efficency here. Sure in some cases Flash might be better but Ghost is a lot more fun.
I take Cosmic Drive into pretty much any build because movement speed works too good with Lillia. Once you have enough abillity haste and mana sustain you can maintain your passive stacks up and once you get your Cosmic Drive going you'll understand why it feels almost mandatory to buy it every single game.
You see that I put down 3 levelling paths to take with Lillia. If you go the route of upgrading E first just know your Q won't be that good on it's own with only 1 point in it. On the other hand I recommend upgrading E second into match-ups against range champs. Or you can try putting 3 points into E before finishing your Q.
When to use W? Use it when you're sure you'll hit the center. Please do not use W just because you can. While you hit them for 70-240 damage they can hit you with double or even triple the amount because you decided to waste your time with W. If there's 1 abillity that is hard to utillize is her W. Her E isn't as hard to use as some may believe. You can just yeet it towards a general direction and very often you will hit an enemy so just be mindful when using your W.