Most people, when you say you're going Lulu top, will start to rage. That is only because they do not understand the power of this champion. With her CC, shield, poke, mobility, and ultimate, she is the hardest champion to counter in the entire game. And where do people usually try the hardest to counter their opponent? In the top lane.

Now, there are a lot of builds that can work with Lulu. The obvious support build, flat AP, AP/ASPD, AD Carry, and the build we'll be using, AD On-Hit. Out of these, I'd say the strongest is AD On-Hit, and that is why I am recommending it. Because you only have two damaging spells, and they are on fairly long cooldowns, an AP build just isn't that effective. Even with the new Nashor's Tooth, your damage can't compare to using an AD build. As for On-Hit versus standard AD Carry, you're going top lane. You need survivability, and on-hit items tend to grant that. Your final damage output might not be as high, but you can bait the enemy team harder than AP GP OP.

Pros:
Tons of CC
Difficult to counter
Can build tanky and still deal lots of damage
Can build damage and still be fairly tanky
Extremely useful in teamfights, even if not fed

Cons:
Not much burst
Weak last hitting
Very mana reliant

The hardest part of laning phase for Lulu is your mana management. Your spells have a high mana cost, so it is best not to spam them too much. Instead, harass with your auto-attacks. Use your E to shield against poke or your W to disengage against gap-closing bruisers, then throw some damage back with your auto-attacks. If you run out of mana in the early game and your lane is not pushed toward the enemy's side, you will be in trouble because you won't have a chance to recall.

As for matchups, these vary in difficulty. Your easiest matchups are melee champions with no gap closer. Champions that come to mind include Olaf, Vladimir, and Warwick. You can auto-attack harass them every time they try to last hit a minion, and you can easily win a trade with them using your shield and/or polymorph.

The hardest matchups will be against champions with difficult/impossible to dodge gap closers, such as Jarvan IV and Jax. This is true of most ranged tops. Your best bet against these is to pay attention to the health of your minions. When you have low HP minions, you can wait for the enemy to last hit, then harass. If your minions are all above half HP, you should stay back and try to last hit if you can, because this is the opportunity for the enemy to engage on you. If they do get the jump on you, do your best to disengage with W and protect yourself with E, then counter with a Q and some auto-attacks. You should be able to come out even in most trades with them. Once you hit level 6, they aren't as much of a threat because of your ultimate, but levels 1-5 will give you a challenge. These champions are the closest Lulu has to a counter.

Hopefully by this point in the game, you should have your Wit's End finished. If you're decently fed, you'll have your BoRK finished as well. This will give you decent pushing ability by Q'ing a wave and auto attacking to clear the creeps. This, in turn, gives you versatility. By design, you are best if you are with your team, helping in team fights, but if you feel a good opportunity to split push you can do so at this point. Just be sure to ward and not get caught. Your entire kit will help you to escape if someone comes after you.

You should be with your team during this phase of the game. Teamfighting is your strength and you need to make use of it. You don't have the raw AD to backdoor turrets with your on-hit build. Instead, help win teamfights and push to win that way. Your ultimate is one of the strongest teamfighting skills in the game. Ult your tank as they initiate to knock up the entire enemy team, or if your ADC is getting focused, ult them to peel and keep them alive longer. If you are using the full damage build, you should be staying near the back, shooting whoever is closest to you. It doesn't matter if they're the tank, you have a Blade of the Ruined King to melt their HP anyway. Keep yourself and your ADC alive as long as possible using your spells. If you're using the tanky build, you should either peel for your carry if they are fed, or dive the enemy carry if they're fed. Eventually, your team will win enough fights to push to the enemy nexus and win the game.