So I look at guides sometimes, and see all the same things. Engage with -> -> -> .

I don't do that, but I will show you what I do.

Pros

Too many stuns.
Passive helps your ADC get fed.
Has a lot of compatible carries, with not a lot of counters. (listed below)
Anti-Gank
Anti-Yi
Eclipse scares the push out of EVERYONE.

Cons

If countered, generally hard countered.
She's a maneater

Greater Mark of Fortitude gives 31.23 Health on start, which sounds small, but offers a lot of help early-game.

Greater Seal of Resilience and Greater Glyph of Warding are a helpful defense rune set, giving a bonus 10.26 armor and 12.06 magic resistance on start.

Greater Quintessence of Fortitude offer 78 Health on start, totaling with Greater Mark of Fortitude to give a helpful 109.23 health on start.

Masteries are the usual tank set - 0-21-9

It offers loads of health on start, and Juggernaut might just save your life.

Depending on what summoner spells you pick, you might want to swap for Summoner's Wrath, or Summoner's Resolve.

Start:
sight ward Is the traditional support start.

1st Back
Don't go back until you have 850 gold. Grab a Heart of Gold, or Ruby Crystal if you died, and don't have enough for the Heart of Gold. If you have only 350 gold, just get Boots of Speed instead. Spend all spare money on potions and wards as you see fit.

2nd Back
Don't go back before you have 620 gold, or stay till 980. If you have 620, take philosopher's stone Philosopher's Stone. If you have 980, grab the Philo Stone and some Boots of Speed if you didn't on first back.

If you got Boots of Speed on first back, take Ruby Crystal or Heart of Gold, depending on how much money you have

If you got Ruby Crystal on first back, upgrade to Heart of Gold, and grab Boots of Speed if possible.

Third Back
Upgrade your Philo Stone to Shurelya's Reverie, or Kindlegem, depending on how much money you have. If you can only afford the Kindlegem, get Shurelya on Fourth Back instead of boots.

Fourth Back
Get Ninja Tabi, or Mercury's Treads depending on enemy team composition. If enemy team is well balanced, take whichever unique passive you prefer.

Once you are that far in, you are likely going to be starting teamfights soon, are already teamfighting, or the enemy team has surrendered. Nobody pays attention to backs when not in the laning phase, so I'm just going to explain the build now.

Starting Items: sight ward

Core Items:

Build Finishers:

Locket of the Iron Solari is a great item for helping deal with that initial burst in teamfights, however, it has less health than Randuin's.

Randuin's Omen is a great anti-carry item. Using it's active in the middle of the enemy team can be devastating. It slows their move speed and attack speed. It's passive is also great if you're being focused down often.

zeke's herald Zeke's Herald is a great item, helping your AD Carries with attack speed and life steal.

Guardian Angel's passive can be very helpful, but also somewhat useless, depending on the circumstances. If you die towards the beginning of a teamfight, you are probably going to die as soon as you respawn. If you die in the middle of a teamfight, you may or may not die, depending on whose team is winning the fight. If you die at the end and the enemy wins, you're dead meat. You might also want to get it for the armor and magic resist.

Thornmail is great if the enemy team is heavy AD, but is otherwise useless.

Force of Nature is great if the enemy team is heavy AP, or if you want loads of health regen.

Warmog's Armor is a great item if you want loads of health to keep you up and running.

Leona is hard to counter, but when countered, is generally hard countered if at all. Please note that Leona has no definitive counters, it depends on how well you and your enemy counterpart play.

For instance Alistar counters Leona, yet if that Alistar isn't up to par in their playstile, you could roast that sucker on a spit.

Or if Malphite decides it's time to derp out and try a new build because he's a counter to Leona, he's got another thing coming.

But if either of them are good, *Your Leona evolved into Yorick* *Yorick uses gravedigger* *Enemy Bottom Lane puts Yorick in grave by using kill*

In other words, unless you figure out a way to counter them, they will screw you over.

Remember, communication is key. If you're countered and don't think you can win your lane, tell your ADC to stick to the turret. Diving Leona is almost impossible.

ADC matchups sometimes don't really matter, because either you, or your ADC are really good. In other cases, you might want to consult this little doohicky here.

Great Matchups

Varus. Varus is a great matchup with Leona, especially if that player is particularly good.
Vayne. Vayne sucks, unless the player is good.
Ezreal. Ezreal will gladly feed on your bottom lane counterparts, so long as you make sure to Zenith -> Daybreak
Corki. Corki/Leona requires skill to combo, but just kills if it works.
Xin Zhao. Xin Zhao sounds like it would be a wierd combo, but you just camp in that bush together, jump out, get kills, bish bash bosh PENTAKILL.
Ashe. Ashe is simply a great pick. You can probably take bottom lane pretty easy, especially with that double clairvoyance (clairvoyance + hawkshot).