Hello fellow summoners.
I am BillPhoenixBlade and I am here to teach you how to counter almost all mid lane champions through a lot of lane sustaining through Health and Mana regeneration.Also,while getting in duels,ganks or fights,deal significant damage and stuns,securing kills for your team,and be able to escape like a boss,without using yuor Flash spell and instead use your Zenith Bladeon the last champion and make them rage like you survive with 3 hp from an ignite.Anyway,let's take a look to the items,masteries and runes you're using.

I am using some offensive masteries so my Abilities won't deal low damage in early game and a lot more defensive ones in order to stay in a lane while regenerating your health and mana,so you can farm a lot of creeps,outfarm the enemy AP mid champion and waste the jungler's time while getting ganked,slowing him with your Rylai's and your Eclipse.

Some Magic penetr. Marks will help you,while synergising with your Abyssal Scepter in late game,while your defensive seals and Glyphs will help you be resistan towards enemies and sustaining your lane.Also,some more mobility with your Movement speed quintessences in order to wither get in teamfights after being away or getting out of dangerous situations that may cause you to lose some creeps and lose your tower.

Heavy ability power items in order to cause them a lot of trouble to the enemies with your AOE spells.In duels in mid lane this is your combo.Hit an enemy with your Zenith Blade.Immediately after hitting him,activate Eclipse as long as you are in the air.Then stun him with your Shield of daybreak and let him take your Solar Flare right in the face,getting stunned once again and swallowing your Eclipse damage,sending him to his early grave.If he doesn't die from one of your E-W-Q combo,you'll be able to ue another one with your health and mana regen masteires.Note that the items are defensive too since they give you a lot of survivability.

Flash will help you get away from ganks or get in range for your Eclipse to damage the enemy if he flashes riht after you use your Zenith Blade.Ignite is good so you'll kill enemies who will get away with low health and you won't be able to reach him with your other abilities.Ghost,Teleport and exhaust are helpful as well,but with Flash,Leona becomes unstoppable,using it to escape a load of CC,ganks and everything else while she keeps ablaze the enemies with her Ultimate.

==PROS==
-Awesome burst damage
after you grab her ultimate
-Great duelist
-Counters a lot of mid champions
with her mobility

==CONS==
-Very low damage early game
-Hard to farm in early game
-Needs a lot of Mana

Last hitting with Leona is kind of hard until she takes both her Zenith Blade and her Eclipse.You can use your Solar Flare though to pulverize minion waves since it's low cooldown.