As any support i personally prefer Exhaust so enemies can hardly run but when i have to play against Champions with a Strong Escape like Ezreal for example i usually take Ignite that i use when they are with half HP in early game in they way i dont steal the kill to my ADC from the moment i'm supposed to feed him and not my self.I guess why i took flash it's clear it's a "Save-***-skill" or good for chasing.

I decided to build "My ideal Leona" full tank so as well in early and late game i want her able to tank for enough time as i choosed Magic Resist and Armor Marks,Gylphs and Seals,I decided to took HP Quints mainly for late game i don't think Leona need mana regen runes because it's not really a problem after level 6 also not HP regen one as she already has a good HP regen.

Eclipse(W):
Cost: 60 Mana
Range: 450
Leona raises her shield to gain Armor and Magic Resistance. When the duration first ends, if there are nearby enemies, she will deal magic damage to them and prolong the duration of the effect.
Gains 25/35/45/55/65 (+0) bonus Armor and 25/35/45/55/65 (+0) Magic Resist for 3 seconds. When the effect ends, nearby enemies struck take 60/110/160/210/260 (+40% Ability Power) magic damage and Leona retains her bonus Armor and Magic Resist for 3 seconds.

First skill to use until level 6,when you get your Solar Flare use it first if the enemies are close to each other then Zenith Blade--> Shield of Daybreak--> Eclipse and then escape if they are not just do


Zenith Blade (E):
Cost: 60 Mana
Range: 875
Leona projects a solar image of her sword, dealing magic damage to all enemies in a line. When the image fades, the last enemy champion struck will be briefly immobilized and Leona will dash to them.
Strikes all enemies in a line dealing 60/100/140/180/220 (+40% Ability Power) magic damage. The last enemy Champion struck will be briefly rooted and Leona will dash to them.

I usually start to engage at level 2 if I have an ADC that do a decent damage in early otherwise I wait to level 6 or for the jungler to gank but anyway this is the second skill to use,It's a really strong dash with a nice range at all.

Shield of Daybreak(Q):
Cost: 45/50/55/60/65 Mana
Range: Self
Leona uses her shield to perform her next basic attack, dealing bonus magic damage and stunning the target.
The next basic attack deals an additional 40/70/100/130/160 (+30% Ability Power) magic damage and stuns an enemy for 1.25 seconds.emy for 1.25 seconds.

This skill need to be used after Zenith Blade(E) Leona stun the target,i usually use it also to save the *** of my ADC when he got chased from the enemies

Solar Flare(R):
Cost: 100 Mana
Range: 1200
Leona calls down a beam of solar energy, dealing damage to enemies in an area. Enemies in the center of the area are stunned, while enemies on the outside are slowed.
Calls down a radiant beam of solar energy dealing 150/250/350 (+80% Ability Power) magic damage and slowing enemies by 80% for 1.5 seconds. Enemies in the center of the flare are stunned instead of slowed.

Leona's Ulti is really op in my opinon if the enemies are in the center it works as a stun if they are at the edge it works as slow with a really nice damage,if i want to engage with it i usually hide in the grass and try to stun both adc and enemie support then i go again on the adc with E+Q.

Relic Shield: With the new patch the final item [Face of the Mountain] got re-worked and it became really OP from the moment the shield you can give to your adc came really powerfull and also the time for the additional farm was reduced so evolve it after you picked the sightstone.

Doran's Shield:This start will make you stronger if you plan to play aggressive but at all it will make your farm really lower.

Ruby Sightstone:As all the support you need to ward the bash around to see if the jungler or other lane are coming to gank you or when Dragon and Baron get killed,that's why you need to get as soon as possible Sightstone and Later evolve it in Ruby Sightstone.

Sunfire Aegis:I think this item make Leona really OP in team fight because it gives you a nice amount of HP and armor plus it has a nice passive that is usefull when all the enemies throw their self on you.

Mercury's Treads:As Leona you will have a really low mobility that really bothers in early even more in late that's why i usually prefer to close boots first of the sun fire.

Randuin's Omen: I take this item always because it rise up your armor and hp and plus it got a really good active use,it slows the enemies and low their defence/magic resist,so it's really usefull for dont make them run or to use when you are in danger.

Banshee's Veil: Usually in all the match you play there is at least one Ap champions so that's why it is really usefull. I love this item because of the health regen and as well because you don't take damage at the first attack the enemies hit.

Locket of the Iron Solari, Spirit Visage, Zeke's Herald:Those are situational item it depends on how much your and enemies team are feeded usually i pick Locket when the other team is more feeded so at least i can offer to my team more protection and block more incoming damage,at all it depends also on how many AP/AD carry you are against.

-Leona is really strong tank and i think one of the best support at the moment but for example i found her really weak against a well played Alistar cause of his Trample and Pulverize that make her little usless.
-Leona offer a good control of the game and lane.
-In early game and also in late she is really slow and so it takes a little to reach your mate.
-She has a short list of counter (personally only one i was unable to play against is Alistar and a little Lulu) that's why she is so used.