Glitterlance has a fairly low mana cost, meaning that you can use it often in lane to harass.
You can use Help, Pix! on allies, enemies, or minions in order to greatly extend the range on Glitterlance and make an unexpected assault on an enemy champion.
Always be careful when using Whimsy. The speed boost and bonus AP on Whimsy are both very useful, but using it defensivly may mean that it isn't available to cast when you find that you really need it to disable a high damage enemy such as Talon, or Riven, or to interrupt a channel such as 玛尔扎哈的Nether Grasp or 费德提克的Drain.
Lulu excels at supporting initiation: attach Pix to a tank, then Whimsy them to allow them to move into range of the enemy quickly and fire off a Glitterlance to slow much of the enemy team.
If the tank already can initiate (such as Malphite), you can instead use Whimsy on yourself for bonus AP.
If so , use Wild Growth and you will disable the entire enemy team for a couple of seconds
Wild Growth has many uses. It can enhance an already disruptive tank with its knockup and slow, make a bruiser virtually impossible to peel off an enemy carry, or even protect a carry of your own. In lane, it can make ganks from champions with a leap or dash ability deadly, or be used to escape enemy ganks. In general, it should be used early and often as its cooldown is far shorter than most ultimates.
Wild Growth does not grab turret or minion aggro when used on an allied champion, knocking up surrounding enemy champions. Thus it can be safely used within turret range.
Wild Growth isn't affected by healing reduction because it will increase health, not restore it.
Lulu's abilities have a good base but scale only moderately well with Ability Power. And since much of her effectiveness comes from enabling and disabling others, Cooldown Reduction will allow you to be more effective then getting straight AP.
At 40% cooldown, you can constantly keep Help, Pix! on an ally.
Lulu can easily support other champions from the back, leading her to use aura items.
Mercury's Treads reduces both her disables, as well as her damage output. Making them an ideal item.
Lulu does not have a very high natural damage output, so when alone or focused, she'll die quickly without much retaliation.
She however ,has a much higher damage output than any other support so don't ignore her completly.
In lane, Lulu will often harass heavily with her Glitterlance. Unlike many piercing skillshots, standing behind minions will not mitigate the damage, so moving erratically can help mitigate damage taken.
Lulu has no consistent heal, so poking at her or her lane partner will chop down their health or waste Lulu's mana trying to shield them.
Wait for Lulu to use Whimsy before trying to use any channeled abilities or heading into the fight. This leaves her without the polymorph or speed and ability power buff, and allows your team to fight without disruption. Whimsy has a fairly high cooldown, especially at earlier ranks, meaning you have a good amount of time to fight before Lulu can use it again.
Watch out for Help, Pix! as Glitterlance's second bolt will fire from Pix's position, meaning that Lulu can pick up an unexpected kill on you or a nearby ally if she tags you or a nearby champion/minion with it.
Despite Lulu being squishy , she is extremely hard to catch , as she will escape with Whimsy , slow you with Glitterlance , prevent some damage with Help, Pix! and if you get too close she will send you flying with Wild Growth
Try to get Lulu to waste her ultimate without her team initiating. If Lulu uses Wild Growth in conjunction with a great initiating champion such as Malphite or Maokai, your team will be locked up for a few seconds.
If she does use it, be careful of what you do next.
While the knock up, health, and slow are disruptive, they don't hurt your team much after the initial knock up, so staying and fighting may be a good option if you can take out the champion before Lulu can shield them or give them the ability power and speed buff from Whimsy.
If you have to run, beware of the slows from Wild Growth and Glitterlance. If you get slowed by both of them, a polymorph from Whimsy may take you out if Lulu's team is nearby. Also keep in mind that Help, Pix! extends Glitterlance's range, making it a very effective chasing tool if she attaches it to you or a nearby champion/minion.
Finally, remember that Help, Pix! reveals a tagged enemy champion until Pix leaves, making it impossible to juke through bushes or past corners for the duration of the debuff.