I peaked this year at d3 100lp playing support primary, with Lulu (when not banned :s) be my go-to primary pick. I've been wanting to do a guide with Lulu to help everyone improve playing her, as she can massively influence games.
**Runes, Masteries and Summoners**
Runes: Early AP is important as Lulu's early game is incredibly strong.
CDR is also important, despite Lulu's build often clearing 45% CDR easily.
You'll also likely want some Armor/MR for lane.
Masteries: In the majority of matchups, you'll want Thunderlord's for lane pressure. Into a small amount of matchups you can take Windspeakers (facing Janna/Cait etc) where there is near no kill pressure or trading.
Summoners: Again I believe in the majority of lanes where there's kill pressure, ignite can be vital in lane. Exhaust is not often needed due to Lulu's kit giving her so much peel. Yet again if you're against a Yasuo - Yi - Kassadin - Cait - Janna then by all means take exhaust.
I believe that the E start is best for Lulu. It can be used for shield or damage, and isn't skillshot reliant like the Q. Getting full Q damage off is rather difficult due to the reduced damage after the first hot.
Your ideal trade from level 2 onwards is the 'E auto Q thunderlord's' trade. This does a deceptive amount of damage, and is on a low cooldown. It also makes the Q massively easier to hit, as Pix is on the enemy.
If lane is going well, you can put an additional point into E instead of W at level 3. The early polymorph/speedup isn't overly vital if you're harrassing well, and the extra damage can suprise your opponent into an early FB.
I find these to be the most difficult to play on Lulu for a number of reasons
1) Despite E max, base damage falls off leaving Lulu no longer be a true damage threat.
2) 1-2 points in W leaves the attack speed buff/polymorph minimal, as well as a large cooldown.
3) Not much CDR built up at this stage, probably maximum of 25% which leaves your utility on a long cooldown.
4) Not much mana regen built up for E/W spam on carries.
As far as I can tell there isn't too much to avoid this. The best way would be to either attempt to roam and help lanes, or stick with the AD and lane to gain XP and gold to get past this lull.
This is where Lulu absolutely shines. You should have E, W maxed with 2 points in ult, as well as 45% CDR and huge mana regen.
There is almost no cooldown on your E or W, and you should have 2 or all of Redemption, Locket and Ardent Censor.
Assuming your ADC isn't too much of a donkey, your entire focus should be on buffing them and keeping them alive. Lulu's kit synergises so well with auto attackers, so keeping them alive will inadvertantly give them huge extra damage.
It may be tempting to ult that Maokai to get the 3 man knockup, however you may then neglect your ADC while a Kassadin flashes onto them, which is more important. You should always be positioned just behind them in a teamfight, and keep track of everything that may be trying to kill them.
'W' usage: This is one of the most important things; do you polymorph, or do you give huge attack speed?
This should be determined by both team compositions and the state of the teamfight.
1) Does your team have a big frontline still alive?
2) Does the enemy team have any notable assassins who need to be silenced?
3) Is the enemies front line a huge CC threat that needs to be focused?
Own team has Irelia, Zac, Viktor, Caitlyn, Lulu
Enemy has Nautilus, Lee, Syndra, Lucian, Tahm Kench
The enemy back line (Lucian, Kench, Syndra) should have their time at the start of the fight taken up by Irelia and Zac.
Lee Sin and Nautilus are going to be trying to find ways to CC the ADC, and are the primary 'W' target at the start of the fight.
A Syndra ult is the only real burst which needs to be worried about, and will be the target that needs ulting.
Ideally, the Lee should be W'd first, as his CC is a bigger displacement, which could be the worst result for Cait.
Once Lee is dealt with, the next W could be used on Cait to give the massive attack and movement speed to kite/avoid further CC from Naut/Syndra.
A final W can be used on one of the enemy back line, to stop a huge threat from hitting for 2.25s.
This entire time your E should be on Cait for shielding, Pix damage and Ardent Censor damage/AS.
You are not expected to be putting out any damage at all in later teamfights, but your role is to solely protect. If this role is completed to perfection, you can buff up an ADC so much that they will win a fight, almost disregarding anything.
Hope y'all have fun using a fun champ that has an incredible early game, and can keep an ADC alive through anything, and as a duo lane can carry every game.