NOTE: I haven't tried this after the buffs yet (at least, not properly) but I think her laning went much better and now you have to reconsider it. Still, I'm sure the jungle path still works.

Since she was released, Leona has been considered and UP champ by most competitive players, and you know what? They are right. Realize that, she lacks the power off-tanks have. She has poor ratios and her spells are meant to buff only one thing-> Tankyness!

Her role is to be a full tank. In the current meta there's only one pure reliable full tank-> Amumu. You are not at his level, realize that, but Leona is a safe option in case you need a full tank in the jungle and you can't/don't want to pick Amumu (or Jarvan IV). When will that be? You get double AP carry. You need good CC to keep 3 carries alive and you need a good initiation for that. And THAT you can offer to a team.

But... why play Leona in the jungle? Well, as I said, she's quiet UP for the current meta. She's better in a duo-lane and she can do good enough in bot-lane, but a good ad+support lane will destroy her and her carry (tho you can quit farming you will have troubles vs good laners). Mid is not an option, you can't farm vs ap carry. You can't trade damage. Not your place. Top is just like mid. Any proper off-tank will outlane you hard and you can't do nothing about it.

You are kinda item independant champ. You got pretty high hp pool and your Eclipse is a great resistance steroyd. The jungle will give you just enough gold to keep you going and the reason you are good there: YOU GOT AWESOME GANKS! That's what makes you viable in the jungle. Always remember, if you can get the lane to burn flash you give your lane partners advantage over the enemies and that's a SUCCESS. Ofc it's better if you can get the kill but don't be greedy. If you die it just doesn't worth it as the time you are not jungling, you are not a threat and the enemy laners will have advantage over yours.

Lets get started with this.

Okay, the OMFG you are completly crazy. Well, I actually am not. Why this rune setup? Well, you need it in order to jungle properly. I tried to get the most powerfull minion killing set up so your jungle speed is as fast as possible. This will put some dmg on early ganks too which is where you lack your potential so it's all good. 25 more armor late game won't help you but this AD and AS early game will definetly help.

I've tried more tanky set ups and they would always make my jungling a nightmare, keeping me underleveled and low hp which would stop your ganks and that's not acceptable.

My standard Jungle-Tank set up I use for Amumu, Rammus and Malphite. Gives you HP for safer ganks, armor, mres, xp buff... Nothing special about it.

Okay, this is an important part of the guide. The path with Leona is quite flexible after first camps but you have to play it safe and not be greedy, if you try to get as much XP as possible you will not be able to gank. And if you don't gank, you failed hard as a jungler. You can gank after your first trip around the jungle very effectively. Try to do so if it's possible, even it only scares the lanes, but remember, play it safe.

Jungling path:

1-Smite Blue Wraith: You can do it in your own Wraiths if you want to play it safe but you can also do it on enemies.
2-Wolves: Focus big one. One or two Eclipse should be enough.
3-Wraiths: Focus big one if you didn't smite your own Wraith.
3.1-Little red-buff lizards: ONLY if you feel greedy and you can't see any easy ganks after golems.
4-Golems: Smite is ready again! Use it.
5-Gank time! If nothing can be ganked go back, but I'll be sad if you do so :(

HINT!: Remember that your Q resets your attack timer. Use that in your advante for faster camp clearing ;)

After a couple ganks or more jungling you should be able to grab Madred's Razor. Now you can start clearing buffs and camps faster than a bullet with no problem. You can try buffs without razors but you'll be SO low HP that you will have to insta back and, trust me, doesn't worth it.

And remember: GANK GANK GANK GANK GANK! That's what you are strong at.

This is what I thought when I saw Leona's spotlight: OMFG! GANKS! As a usual jungler I know that almost any champ can do it effectively if they have a good enough ganking potential. The mechanics are pretty simple:

Pop out from a bush with Zenith Blade and keep your stunt going with Shield of Daybreak. Your passive will help you stack good damage along with your team. If you land your E and can complete the combo (and your allies are smart enough to burst their dmg on your target which, unfortunatly, isn't always) it'll mean 80 to 100% of enemies HP. Remember to load your W one second or two before the gank so you can stack your burst much faster but try to always give time to your mates to burn it!

Starting Items

This is basically for faster jungling. Leona has high enough base stats to keep her going high HP (REALLY high actually which is good for our GANKS) and the jungle speed you get with the sword is amazing. The pot is always good if you see your hp dropping low and you wanna risk in a gank.

Core Items

Philosopher's Stone

This is basically your core items that you want to get 99.99% games. Provides you with movibility for early game ganks, fast camp clearing and some good amount of gold with actually ver usefull items. After you end this, it's pure luxury.

Completing the build

The items listed are just item I usually get with any tank at all. You will have to choose them depending on enemy team.

Boot choice

Okay, here you have 2 options:

MY CHOICE

Right now, Leona has REALLY long cooldowns which makes you an initiator. The problem is that you lack damage to be usefull after the combo. That's why we need heavy CDR so we can abuse our stunts (and our passive) as much as possible. We can get tenacity out of Eleisa's Miracle so it's all okay.

NOT BAD CHOICE

If you think your cooldowns are okay and that another free space in your inventory worths it more go for it, but NOT my choice.

I will try to keep this one short so I won't write more. If you want me to add more chapters I will. Remember that my thoughts were to make this a JUNGLING guide that's why i didn't go into much detail with teamfights and so. But if you want I can add more information. Good luck and have fun with this pretty pretty girl ;)