I am a gold Zyra main with over 600k mastery. Feel free to check the stats in my League of Legends profile; my season stats are comparable to the best Zyra players in the world.

I am not a League of Legends master. I'm not making this guide to tell you how to play League. The one thing I really DO know, is how to play Zyra, and what works best on her.

Take this guide, combine it with guides on the game, or your own knowledge, and excel. My Zyra game is worth being noted.

As a support, your ideal goal is to protect and help your ADC. Exhaust is a great defensive to have on Zyra. If you'd rather play super aggro, Ignite is an option; but trust me, you do enough damage without it.

Flash is not optional.

Electrocute is huge damage early as Zyra. This makes you a huge lane bully, and increases your early kill potential (thus leading to faster boots, too). Laugh at lesser Zyras who take stupid choices like Comet.

Cheap Shot, of course, snare effects for the win.
Zombie Ward, if you don't suck at killing wards. If you play mindlessly, just give up and take Eyeball Collection. It's worth doing Zombie Ward RIGHT if you're going to do it.
Ultimate Hunter! Recent buffs to Zyra have decreased the CD on her ult already. Enjoy wrecking enemies and being the hero of your team fights that much more frequently.

Magical Footwear, as discussed in itemization, is a great choice and a support budget gold saver.
Cosmic Insight, with the scaling CDR, will give you 45% CDR with this build.
Adaptive / +HP, for the early game edge.

The pros start Q. I get it. It's a far less obvious skill shot, it's more difficult to dodge, it's less predictable, and the range of the spitter is more early damage.

I'm a Gold player. I'm not fantastic, but my Zyra game is. Playing Zyra into other Gold players and below, it's not hard to hit her snare. If you are at an ELO that you're looking up a guide, there's a very real chance your opponent won't dodge the snare.

I max E first because when you snare enemies in your ult, and throw some seeds in front of that snare, those plants hit like a truck. Add in Liandry's passive. You delete people.

If you're a mid lane Zyra, you're going to max Q first. If you're a pro, you'll probably make a choice based on your opponents, but there's value in maxing Q, obviously. If you're a support Zyra in a middling ELO, max your E and laugh at the noobs who don't predict your moves or can't sidestep.

The obvious support item choice has to be Spellthief's Edge, but you should never bother to upgrade it beyond Frostfang (unless you're full build). You get 3 charges of a ward on Frostfang anyway; on a support budget, the additional 950g to upgrade isn't worth the 15 AP.

Keep a control ward up at all times. Prioritize location based on your opponents (and on your ADC's warding habits). I tend to pop my control ward in tri bush on blue side (place it towards the left wall), or the gromp/tower dive bush on red side (place it towards the bottom to allow vision on blast cone). Those are long term investment locations.

When you're against a Twitch (or some other obnoxiously invisible champion) it may be worthwhile to control ward the bottom brush. Additionally, if you're feeling aggressive, control warding the bottom brush can also bait out a fight.

Aside from these obvious support staple items, the next thing you want to build is the biggest AP piece that contributes to Rylai's, Liandry's, or Luden's (more explanation to come later).

You will be taking Magical Footwear, in this build. Yes it's frustrating to wait out the boots, but as Zyra, your early kill potential is so good that those boots will end up coming earlier. Having the additional 10 movement speed from Magical Footwear is great, later in the game.

There is absolutely no other reason to ever get boots other than Sorcerer's Shoes. Magic pen is awesome on Zyra, and it ends up being impactful into any team comp. You are a glass cannon. Merc treads or tabis "defensively" is outright stupid. There is some argument to be made for Boots of Mobility, for more roam potential, but I will always opt for Sorcerer's Shoes.

You will almost always end up purchasing all of these four items, and along with boots and your support item, these make up the entirety of your full build. There are some exceptions, which I will get into, but let's start here. Prioritize these items based on the following scenarios:

RYLAI'S - DEFENSIVE. Your best defensive support item will be Rylai's. The slow applies to hits from your plants. This gives you better utility by allowing more escape for yourself and your teammates. It can also be used to help close gaps in an engage. Most importantly, it allows your fellow AP-using teammates to prioritize Liandry's, and to get the full effect of the passive based on your Rylai's slow as the required movement impairing effect.

MORELLO - THEY HEAL. Rush Morellonomicon when you are facing a team with heavy healing. Draven with Bloodthirster, Vayne with BorK, a fed Nami or Sona, Senna... when the enemy team has a Volibear, Swain, Mordekaiser, etc. The list goes on. Grievous Wounds is always something you should prioritize in situations where you can impact healing potential. If you haven't witnessed the value in this passive, or think you can just out-damage it, let this be your wake up call. Never go without it against a heavy healing enemy team.

LIANDRY'S - THEY'RE TANKY OR YOU'RE THE CARRY. This is huge damage for Zyra. Huge. I cannot stress enough how big this damage is. Your E, the slow from Rylai's... this item is such a necessity. You should always build this into a tanky team, but in reality, you should always build this, period. Whether or not you rush it is based on how tanky they are. I see a lot of Zyra players rush this item purely as an aggressive choice; it's not my first choice for being aggressive, but I do understand the logic. An aggressive rush on this item is a play style choice.

LUDEN'S - YOU'RE AHEAD (or just meet your CDR max). With this Zyra build, you will get 45% CDR. If you're ahead early, and can afford it, get your Lost Chapter for the mana regen. You can finish off Luden's at your convenience; once you have Lost Chapter, it would be more valuable to finish one of Rylai's, Liandry's, or Morello before going for the full Luden's.

If you have the luxury of building one or both of these items, you will definitely also still have Luden's Echo.

If the enemy team is building heavy magic resist, it may be worth substituting Void Staff for one of the other items on your list. Realistically, you'd substitute Rylai's for it, because both Morello and Liandry's would still be useful into a heavy MR team.

If the enemy team is letting you stomp them, pick up Rabadon's instead of one of those items. Drop whichever one works best situationally.

If you end up selling your boots (but I mean honestly, why? Why would you ever sell them? You roam more, you chase better, you escape competently, they give you magic pen -- WHY SELL?) you could probably replace them best with Spellbinder. At least this way you get movement speed, and an on-use movement speed to escape or close gaps, along with a huge amount of AP.