So this is my Leona guide and also the first guide I've written. I don't pretend to be a pro, this is just a way she has worked well for me. Just remember that no build is set in stone and you build for your opponents.

Pros
- High Health and Health Regeneration
- Great teamfight initiator
- Stupidly high armour and magic resist
- Cool character model

Cons
- Passive doesn't help you at all, only teammates (kind of a pro as well, as it promotes teamfights)
- Weak Auto-attack
- Average speed

For runes I like 9 Greater Mark of Magic Resist, 9 Greater Glyph of Cooldown Reduction and 3 Greater Quintessence of Health. Seals have 2 viable options 9 Greater Seal of Vitality or 9 Greater Seal of Evasion. I have only tried the Vitality option but as this build uses Ninja Tabi you could get about 19% evasion as opposed to 175 health, it think its really either, or, however as I also build Thornmail I would prefer them to hit me more often.

Wow so I don't always use the 21/9 setup, but I would rather put points into Masteries that can actually assist my champion, so I have done the strange 3/24/3 as I feel this is the best usages for the masteries. Obviously you are a tank so you will want lots of defense. 3 in Resistance and Hardiness. 3 in Strength of Spirit and 4 in Evasion. Then Nimbleness and 3 in Harden Skin as 1 in Defensive Mastery just to help with mobs. 4 more in Veteran's Scars, finishing off by Reinforce and Tenacity for total damage reduction. I choose the 3 points in Deadliness because sometimes I will also build a Zeal>Phantom Dancer and this gives me a good critical chance also it is a nice surprise when with 2% crit you actually proc it on low levels. Finally 3 points in Perseverence just for more Health regen with a nice little mana regen boost as well.

No matter who I am versing I will always buy a Regrowth Pendant and possibly a health pot if you want to be extra careful. On your first trip back you should have enough money for the Philosopher's Stone and at least lvl 1 boots, obviously the more you can buy in one go the better so if you have the cash grab the Cloth Armor or for 200 more Ninja Tabi. With the gold per 5 item working from that point on play smartly until you can get the next 2 Regrowth Pendant's. At this point you will be alot safer and you can start to push your enemies around. The Giant's Belt makes this easier still. When you upgrade to Eleisa's Miracle is totally up to you, as you do lose the gold per 5 component, so if the enemy is light on cc you may want the bonus gold more. A Chain Vest is usually next then totally upgrading it to Thornmail asap, though remember you build to your enemies os if there is lots of AP finish your Force of Nature first. Goodbye physical damage dealers. Next is straight to Force of Nature unless magic is totally owning you in which case by a Negatron Cloak first. I have barely ever gotten past this point in my build but next I would grab another Giant's Belt and then build it into Frozen Mallet. Then just stock up on potions with priority being Elixir of Fortitude, Elixir of Agility then Elixir of Brilliance and Oracle's Elixir if you are not dying much.

Solar Flare is always a priority so get it whenever available for good damage and slow/stun I find this skill best saved until the end of a fight to pick off the scraps of your impenetrable defense. Eclipse is your next highest priory and also your starting skill in most cases. This brilliant skill is the main reason Leona is a tank. It boosts your magic resistance and armour for 30/40/50/60/70 depending on skill level for 3 seconds. This might not seem like much but the best is yet to come, at the end of this effect the shield explodes in a small AoE for 60/110/160/210/260+ 40% ability power damage and if it hits any opponents even minions, the shield restores for another 3 second for a total of 6. This awesome skill is also your main farming ability after its third level. I like to get an early point in Shield of Daybreak at level 2 unless a teamfight is certain in which case you might want a stun on level one, even then though it might be better to get eclipse for the AoE. After this get eclipse to level 2 then get 1 level in Zenith Blade and you have your Initiation set at this point. Wait in a bush with your team, see enemy pop Eclipse> Shield of Daybreak and then Zenith Blade in. they will be stunned for .5 of a second from Zenith Blade then for another 1.25 from Shield of Daybreak then shortly after Eclipse will pop for even more damage. Continue to level up Eclipse asap unless Solar Flare is available. Do the same combo as above and add solar flare to mop up the scraps. Then level up Shield of Daybreak and finally Zenith Blade. Then Laugh manically at your helpless opponents. The reason for powering up Shield before Zenith is because Zenith is a skill shot and Shield is an empowered auto attack, I feel there are more uses for Shield.

I think there are only three real choices for summoner spells as Leona and they are Flash for the obvious reasons of that even though you are a tank in you are found 5v1 you will want to try to escape and this makes this alot easier. The next is Fortify which is a great tower defense once every few minutes(even more so with Reinforce) but also gives you 9 extra damage vs minions which helps you farm and last hit at earlier levels. The third is Heal which I think is a massively underrated summoner spell if used correctly. Early team fights can be won with a good heal usage and it can also help sustain a push if you have taken some damage.

So have some fun with it and let me know what you think. Look forward to seeing you on the battlefield, maybe even Leona vs Leona.