Lulu is a Support/Mage champion that uses AP to assist her ADC. Alongside with Pix, Lulu can is a support that can help a lot. Below will be the guides and tips of how to use Lulu in my own way. Hope you guys enjoy this guide.

1. Always poke with lulu with your basic attacks. She is really great with poking. After a poke run back to safety and protect your ADC.
2. Most support usually stand infront to protect the ADC, however, Lulu is weak when it comes to defensive plays, so she stands back and helps the ADC.
3. If you are full with Mana but you are scared to poke because of your HP, Use your e on a minion then Q towards the enemy ADC. Always the ADC not the support.
4. Use your W (Whimsy) accordingly to the situation. If you're chasing the enemy, use it on an ally. If he is getting attacked polymorph the ADC as they have the strength of AD.
5. In team fights, I see Lulus use their ult (Wild Growth) on the most tankiest target, but I prefer using it on the most STRONGEST target so then they are durable and have the chances of killing.
6. Take Heal rather and Exhaust because your Q can slow them and you can't really get close to the ADC or Support Champion.
7. It's fine if you die, but if you have your Ult, use it on an ally before you die just in case the opposition scores an ace on your team!
8. Don't take CS and just back up the ADC.
9. Do not roam unless the ADC decides to. But don't always follow the ADC. If you have already won your lane, go roam to mid. You may die but if your mid jumps at them, you are likely to get the kill.
10. Place wards and always be map aware. (Just in case someone ganks)

I just take usual AP runes just for the poke and assistance for your ADC. Armor Seals and MR Glyphs are pretty straight forward. These are to be defensive from the ADC as well as ganks.

For Lulu, I build some AP so I manage to do damage and contribute to the team. And defensive so that if they target me, I won't die so easily and feed in every game.
You're usual starting Items would be Spellthief's Edge, 2 potions, a Stealth Ward and a Scrying Orb.
During your first recall, if you have enough for Ruby Sightstone, GO FOR IT! But if you don't, just get the usual Sightstone and Ruby Crystal (or Boots).
My final build would usually be Ruby Sightstone, Boots of Mobility (Homeguard), Athene's Unholy Grail, Mikael's Crucible, Morellonomicon and Twin Shadows.
Although these items may seem a bit weird, I use it and works great!

For my summoner spells, I take the usual Flash but I get Heal instead of Exhaust. Since Lulu can't get extremely close to the enemy, it is better that you can heal your ADC rather than take a risk just to exhaust.
I don't max spells specifically with Lulu, I upgrade each one all at a time because they are all useful. And of course always upgrade your ult whenever you have the chance!

Lulu can help initiate team fights really well. Although I told you to stay at the back while laning, in team fights, I suggest you stay in the front and protect your team. Even though this sounds risky, your team can't afford to lose your assassin, tank or ADC. Even though you may sound like "I'm support, I'm worth nothing", you're Ult has the most worth and could be dependent on. Ult the strongest target and then use your Q to slow. Then Shield your ally that looks like they're gonna die and polymorph their strongest champion.

Lulu is a great support champion that I recommend you to play. I started off quite bad with her but then got used to her after playing a lot of games with her. She is a pretty fun champion and I always laugh when I see the enemy get polymorphed. I hope to see you guys Lulu and have an incredible experience with Lulu (: