Hallaaa, I'm Petrotes, if you care about that; I was Diamond 2 two season ago, back when ardent censer healed.
Now I don't play too much ranks, but people like my lulu. I guess I'm pretty good.

Lulu is an enchanter that succeeds in singletarget buffing, so she is good with hypercarries (or out-of-control bruisers).

Pros:
-Good against poke
-Good escape with W Q and R
-You are annoying
-Not useless if behind
-Safe pick
-If an assassin without spellshield engages, you can time your R right before it heals damage, then W right after the knockup expires
-You can never mess up with your ult, unless you waste it.


Cons:
-No damage starting from mid-late game
-Can't carry if no one is fed
-No engage besides [E(minion) -> Q]'s slow
-You can bait your carry into death if you buff him in wrong moment
-Doesn't like ganks at all
-You will get flamed along with your adc if you got a bad adc
-No immobilize. Sad samira and caitlin noises

Summon Aery
Good for chad oppressive poke, and for small trades.
She got two basic spells that can proc that on ally, (W and E), so you can proc aery twice in a non-teamfight.
Better in early than guardian, but if you bet on getting your carry strong in early, you don't care too much about the guardian being better later.

And something small but notable: Second aery will benefit from 35% H&S power from moonstone, whereas guardian will not, since it procs first in the fight.

Manaflow band -> mana is nice.
You don't care about magic damage protection from nullifying orb, since you usually die if you get caught by mages, so try to not get caught and enjoy mana.

Transcendence: cooldown is great for second E or Q in fights. Cooldown goes nicely with moonstone

Scorch: You don't roam, and you don't have dmg later, and extrapoke is great.

My preference: Cheap shot.
QAA / EAAQ are great poke combos in lane. Since you have aery and scotch, the 3rd bonus damage is great. If you think you can be super annoying in lane and 1v2 them, pick this.
Ultimate hunter: Lulu's ult is usable in most situations, so lower cooldown on that is needed.

Normal way: Font of life -> usually when you Q, the focus is on that target, and your carry got your attack speed, so more heals from this in lulu's case. Maybe bone plating against catchers.
Revitalize -> shield champ gets a More shield rune.

Now you will see some tips and tricks for each ability.

Q
The slow does not scale with ability level. See this as a good thing: Q has maximum slow possible in all stages of the game. If you land a q, you can continue hitting the target if it got no abilities, since your carry will cover you.
Can be landed easy when you are being chased.
If you got long-range engagers (camile, jhin, renekton, swain), a E(minion) into Q can start a fight in your favour.
You can also EQ randomly to heal with moonstone, and have it stacked if the fight starts.
Later into the game, use Q for the moonstone heal 2 seconds after you E/W.

W
Use this to polymorph enemies with either high dps, or unused burst/escape.
In lane, use this first before the E.
Chain W with your R on assassins to completely shut them down for 3 full seconds (0.75 + 2.25)
Also good to use in lane on enemy carry when they engage. If you poly the enemy carry, keep your shield and use it on your carry after the poly ends. This might bait the enemy into deciding to keep fighting after polymorph.
You can Aery with your W, so you can ardent with W too. Use W then E on 2 different targets when pushing towers with ardent to give the buff to everyone.

E
Block poke in lane, or use it as engage when you think your carry will engage.
E in lane for damage is underrated. Use that if you enter the range briefly. The reason for that is it's instant cast time.
After that, you can go in safe range then Q both of them.
Shield yourself when jhin/jinx/kaisa tries to get canon with W from far away.

R
Most important: After laning phase, use it for knockup/slow for picks even if you don't need the heal.
Big brain stuff:
It is not considered a heal, since it's max health growth.
The good thing: It's not affected by grevious wounds, and you can use it on full health without wasting anything.
The bad thing: It's not affected by heal and shield power.
Sick engage: Flash R yourself and walk with E yourself. W an enemy. Pretend you are morgana. Do that when they have abilities down, and you trust your adc, or they are 3-4 stacked enemies. You will be the malphite replacement for yasuo. Use redemption a little before doing that.

Skip this if you go with shurelia.

When you fight, you should look at 3 things:
Your carry, the minimap, and the moonstone.

In lategame use your q after 2 seconds most of the time to proc moonstone. If you can AA, do that instead of q, and q after 2 seconds.

Usually in fights you want to W the in-combat carry. You will give aery shield and moonstone. Then try to keep your E, and use it after 3 seconds, because aery will come back to you in ~2.75 seconds, and you might as well wait 0.25s for a moonstone stack, then E carry with second aery and second moonstone, wt. If your carry doesn't survive for 3 seconds after w, R them, still keeping your E. Ult doesn't benefit from moonstone stacks, so it's not a waste.
In total, it's 2.21 Aerys, 2.21 moonstone heals, and one stacked E. (3 moonstone stacks give 21% h&s power)
You might think that you waste your passive by keeping your E, but by making your carry survive for that long, enemies will have most abilities down and the carry can basic attack easier.

Of course, this situation applies against normal dps-based champs (nonfed adc or bruisers)
Against burst, you don't really care about moonstone.

In mid-late game you will have enough cdr and mana regen to EQ the wave to safetly sneak some free heal by hitting your q, and also have your moonstone stacked from the beginning, in case a fight breaks out.

This is the main attraction of this guide, so read carefully.

When you lane, you have to bully. Do as much damage as you can. Even against poke (velkoz brand xerath), you just have to dodge and deal damage. If you succeed, they will not poke anymore. If you fail, well, you shouldn't fail.

To do that, you must look at minimap, firstly: When you are aggressive, they will cry for help. If you got your vision nicely and run away, you waste jungler's time. If you don't run, the enemies should be low enough to not help the jungler out, if you are lucky. Be ready to both run away and run them down.


MINION INTERACTIONS
-Ally minions.
When ally minions are low, two things will happen:
>The enemy adc will try to farm it.
>The enemy support will try to stop you from poking his carry.
=> Most of the time you should try to poke the carry but watch out for the support. If you expect the enemy supp to attack you, it will be way easier to dodge.
If your adc is reading this guide, he should attack the enemy support, because it's bussy stopping your supp from poking their carry, and there is no need to farm at this moment. This rectangle relationship happens when you have ally farm low

-Enemy minions
When enemy minions are low, your carry will try to farm. Enemy supp will try to poke him, so you gotta stop him from poking your carry. Watch out for the carry this time

-Both minions are low
This time you should enter predator mode; be ready to dodge, and counterattack if you succeed. If not, use your protection. If they get you, they will engage, so be ready to parry and run. If you can hit q and dodge the supp, you should all in with your friend.

Dancing
Guess what, things are getting more complicated.
In lane, you can stay in topside or botside.
You and enemy support being in opposite sides or same side is important.
Here it comes minion management part 2:
Enemy carry has to farm, so it's positioning will be less variable. We will assume the adc will stay in middle lane.

As I said earlier, when ally farm is about to die, you want to poke enemy carry.
Usually, when you want to poke the carry, you should be in opposite side of lane compared to enemy support. So, when ally minion is about to be low, look at enemy support: If he is on bottom, go on topside. You should form a triangle: you, enemy carry, enemy support, so you can't be hit back easily.

Similarly, when the enemy minion is about to be low, try to be on the same side as enemy support, as he will try to poke your adc, and you should be in offensive, thus you go on the same side to counterattack that.

Remember, same side when you attack, opposite side when you defend.
You attack/defend based on minions. You should make decisions when minions are about to be low and when they are actually low. All this while deciding which to hit, on which to focus on, and who to dodge. And keep looking at minimap all the time. If they go in attack mode for no reason and you don't know where the jungler is, be careful. Try to not give away your jungler position with your behavior. Usually the support is the one that goes in on a gank, because he is responsable with minimap, vision, coordonation, and so on.

1. When you are out of vision: Q E AA
2. When someone missed one of their spells: W (speed) E AA Q AA AA
3. Lvl 1 harass: E AA
4. After you E some enemy, you can back away and AA minions. Pix will try to hit those minions from host position, and will hit the host. Free spellthief gold and free 20 dmg per attack, + 15 from aery, and sometimes scortch.
5. If you randomly land a q, you can W yourself and run the target down. Use the speed to dodge and E for damage if just one of them is fighting back.
6. When you are chased, E Q the carry, and if the carry turns on the slow, W and prepare ult.
7. If you got ignite, flash E Auto q ignite deals big damage, and is point and click, so you can't miss it.
8. If you got exhaust, try to not have both polymorph and exhaust in the same time; chain them together.
9. Once again, R knockup -> W poly is great against assassins.
You will make rengar cry many times.

Thank you all for reading. Might update this. Excuse me if I got any errors here, it's my first guide.
Meet me on the rift, I play on EUNE, ign Petrotes. Let's be friends :p

Big bless to you all.
Peace