This is my first guide and I will post pictures and videos eventually. I play most supports and top laners as well as many jungles, and will post guides for more if you request! Vote up if you like if not vote down but give a response why and I will try to correct anything i can! Thank you all very much.

Leona is a very easy to play support who can secure kills for the ADC easily. Her quick engage style tactics work well with Corki especially because of his built in flash, Valkyrie to jump into the fight. Also Corki can easily ignite Leona's passive Sunlight with Gatling Gun Her early game is very good at level 3+ as long as you have people to follow up with your army of stuns. She works well with a variety of ADC's that play aggressive, and have a built in flash, she is fairly bad with Draven because he cannot jump into battle as quickly as Leona can, therefore her stun is the amount of time it takes him to get into the fight.

Pros:
1. Very fun
2. Takes people from fights
3. Very aggressive
4. Powerful early game
5. Helpful tank/support late game

Cons:
1. Her E can displace you and make you burn Summoner spells for useles engages
2. E range is slightly less then it is shown in game
3. Low damage (Some people want damage doing supports)
4. Easy to see engage in laning phase
5. No escapes in her abilities, if the 3 enemies chasing you and adc are going to get a double suicide to save adc! They are worth much more than you are, jump in and stun i wouldnt ult though.

Obviously Flash is an almost must have, because if you land a bad engage and fly into battle and you cant walk out Flash is a get outta jail free card! Exhaust becuase if you need to catch someone or mid game if you dont have enough damage and you wish to slow their escape. Heal is also viable but like everything, its based on your preference.

Sunlight (Passive): Leona's spells charge any enemy unit damaged with Sunlight for 3.5 seconds. When allied champions deal any damage to those targets they consume the Sunlight debuff to deal 20 / 35 / 50 / 65 / 80 / 95 / 110 / 125 / 140 additional magic damage. This additional damage is counted as the ally's damage and it will benefit from their magic penetration. Leona is unable to activate the additional damage herself.

This is a great passive! You may not be able to see the damage but it does a considerable amount especially early game, this passive is ignited by any spell or auto-attack. Very helpful with killing minions to push a lane or chunking some health on champions.

Shield of Daybreak: Leona's next basic attack will deal additional magic damage 40/70/100/130/160(+ 30% AP) and stun the target for 1.25 seconds.

This is about as useful as you can tell, its a stun! its not as long as Taric's stun but still long enough to mean death when comboed with her ult! Plus it does a bit of magic damage, just a bit.

Eclipse: Leona gains bonus armor and magic resistance (30/40/50/60/70) for 3 seconds. When the effect ends she deals magic damage to enemies within 275 range of her (60/110/160/210/260 +40% AP) If Eclipse damages any enemies, the bonuses remain for an additional 3 seconds.

This is the first thing I max because it gives instant tankyness. The only problem with this is that by the time this explodes the enemy ADC is low and you may steal kills, early game this isnt horrible but a fed Corki can carry a fed Leona cannot.

Zenith Blade: Leona projects a solar image of her sword, dealing magic damage to all enemies in a line (60/100/140/180/220 +40% AP). Leona will dash to the last enemy champion struck, briefly immobilizing it as she does.

This is your engage, be cautious as you may engage under turrets or will be in a bad position when you fly in. Also be wary of who you hit and make sure your Q hits the ADC not the support!

Solar Flare: Leona calls down a beam of solar energy to a target location. After a brief delay, it deals magic damage to all enemies within 250 range and slows them by 80% for 1.5 seconds. Enemies within 100 range are stunned for 1.5 seconds instead of slowed. Magic damage:150/250/350 +80% AP
For the duration, the beam also grants vision in a radius of 350.

I love this Ult, it has a stun, it has a slow, it has vision, a little damage, AND it has pretty crazy range. i wouldnt recomend ulting then E and then Q, but if thats the only engage you can get you may have to or just dont engage. This is a great ult and when you are going in early game just when you get this, throw it just behind them so its a double stun! These stuns will last 2.75 seconds total. Try to anticipate a Flash or getaway, but its impossible to guess an opponents move every time.

I use Seal of Armorx9 and Quintessence of Armorx3 because of the obvious, your bot lane and against an adc who auto attacks so any armor is going to build up your defensive front against them. I use Mark of Attack Damagex9 because it makes you do a bit of extra damage and help for kills in the very early game. You may prefer maybe stacking more armor or Magic Resist, this is your preference. And i use Glyph of Scaling Magic Resist becuase you shouldnt be having an early game encounter with the enemy magic damage, if youre concernced about supports doing magic damage, supports are not meant to do high amounts of damage, if you are really worried or prefer flat MR that is another way to build, I prefer scaling MR simply because at level 12 it excedes the amount of MR flat Glyphs give you.

Obviously 0/9/21, but i have seen a few tank supports go 0/21/9 but i prefer the bonuses that the support masteries give, such as 1 Min ward, Mana buiscuit, gold regen increased, movement speed increased etc. you may prefer also varied points such as not finishing the Utility tree and putting more in defense, once again this is your call, I use the masteries becuase I prefer them.

Starting items are easy enough. Ward around level 2-3 and if you recall when you are low on sight ward get a Sightstone, if you have 2 wards left i get Boots, or start building your Ruby Sightstone, then i get Philosopher's stone becuase its helpful with the bit of extra GP10. I get Warmog's Armor next becuase the health is an instant tankiness that is needed for roaming/laning. I then pick up Runic Bulwark because it gives a very nice aura to help your team out, the same with Banner of Command and Zeke's Herald. Shurelya's Battlesong is a good engage/get away item for your whole team. These items make you tanky and a very very helpful support during the duration of the game.

Ranked Play:

Leona is an amazing support, you need an adc you are familiar with, duo ranked with a friend as ADC and talking to them through skype/Phone etc is very helpful. The skill level of you as leona and your ADC as whoever they play is a key part in your game and a victory or loss! Play just as you would in blind pick with leona, maybe a bit more safe or even more aggressive depending on you.

Team Work:

Leona is the frontlines tank, she engages fights. It is up to YOU to go in or not, remember you do not represent your team when you jump in some may not follow and you need to be ready for that possibility. Use your ultimate on as many people as you can! But that doesnt mean hit the 4 tanks over the fed adc owning you guys. Play smart, know the position of your teamates and if you can jump in or not.

Creeping/Jungling:

Theoretically it is viable and I have done it before its the same skill sequence but I build bruiser, she has horrible cleartime on camps, but her ganks are amazing with the 2.75 seconds of stuns! If enough people comment for it ill make a bruiser guide for fun.:P

Farming:

Dont! You are the support dont attack any minions! If you are pushing use Eclipse to hit them all, I know the Zenith Blade is a faster damage method but suppose your near a turret and you hit an enemy and you dive unintentionally or that you just used your Zenith Blade now you need to engage a fight. So dont attack minions, and if people are pushing just stand there and autoattack they can push without you burning your engage.

Unique Skills:

She can quite literally dive in and stun the ADC, and with a good team win the fight and game! She has nearly 3 seconds in stuns and can turn the fight around! Her Zenith Blade- Shield of Daybreak combo instantly takes a person from the fight and is cruicial to hit the highest damage dealer with the stun.

ADC's with Leona

Corki goes well with Leona because his Gatling Gun sets off her passive, also he can jump in with you with his Valkyrie.
Vayne goes very well with Leona because with the right positioning you can land another stun from Vayne! Make sure not to shoot them out of Solar Flare
Twitch is well with Leona because his poison sets off Leona's passive.
Twisted Fate uses yellow card with Leona and they cant escape!
Kennen Many will probably disagree but ADC Kennen is very good. Leona has 2.75 seconds in stuns but when you add Kennen stuns it is impossible to escape.

Lane situations:

I will post a video in the near future, but Leona is a very aggressive support, at level 3 go in, you guys will win if the ADC goes in with you. The only counters to Leona are lanes that poke your ADC down because if you engage when your ADC is half you will lose, also tank supports counter Leona if your not careful. Volibear is very annoying he doesnt own you guys but if he engages and flips adc go in on their ADC they wont be able to hurt yours when they are stunned. Taric is a counter and thats pretty plain to see. His stun is 1.5 yours is 1.25 so you dont win stuns until 6, but if he uses his stun go in, itll stop your ADC from losing health and maybe even getting some attacks in. Level 3 is the time to draw first blood. Then when they get back you have kills on them and you win most fights you start. Always be aware when your sight ward is going to run out and when you should put a new one down. Also be aware of you're ADC's hp! They do the damage and if they are to low to go in then you dont go in!

Leona is an easy to play, fun, aggressive support that snowballs late game. No matter what point in the game 3 seconds of stuns is helpful, be it when you are level 6 or 18. With firepower behind Leona teams can carry! Hope this helped all of you! Have a nice day and feel free to comment!