Aim Zenith Blade so that the desired target is the last enemy hit by the skill.
Zenith Blade and Eclipse can be used to mark minions with Sunlight to make it easier for your lane partner to last-hit large waves, especially if they have AoE skills.
Beware when casting Zenith Blade near enemy towers; you can be pulled under it and take aggro.
On a similar note, Zenith Blade can potentially put you in a bad position and out of range of your teammates.
Zenith Blade's projectile does have a travel time, so it is generally unwise to use the spell at the tip of its range since the enemy champion has time to dodge.
When laning, control the brush whenever possible as her ability to set up kills gives her excellent zoning.
Using Flash while Zenith Blade is winding up can result in the range of the ability being extended and harder for the enemy to dodge.
If Leona's lane partner is fed enough, and/or they are able to handle a 1 vs 2 lane, she can begin roaming as soon as she purchases movement speed and a gold generating item.
Her massive CC allows her to set up kills easily, especially when Solar Flare is available.
When coordinating a roaming gank with your team's jungler, Leona's ganking ability is more potent.
Leona's abilities have a decent amount of base damage, especially Eclipse. Use this to your advantage to kill fragile characters who underestimate your burst damage.
Leona has the ability to clear enemy wards just after their placement. Deal a basic attack, activate Shield of Daybreak for another, and immediately attack again to kill it.
Leona can be built in multiple ways with the most favorable being a supportive tank. Less common builds include more offense, while utilizing her natural crowd control and tankiness.
With defensive items, Leona can be very hard to kill. Armor, magic resist, and health help her to make a very strong front line. Leona can not only provide initiation, but can also lock down targets with her numerous stuns and immobilizes in the middle of the fight.
Since Eclipse provides Leona a high amount of armor and magic resist, she will generally gain more of a survivability boost from building health as opposed to more armor or magic resist, although the bonus does scale with extra defense.
Relic Shield will allow her to help sustain herself and her partner during the laning phase and builds into Face of the Mountain, which can provide a decent shield and possible nuke depending on who you use the active on.
On the other hand, Talisman of Ascension's active will allow her to engage easier and quicker with her team. The choice can be made based on team composition and the needs of the team.
If you have Randuin's Omen, try to use its active ability while Eclipse is up as the active increases in duration the higher your armor and magic resist. At max rank, Eclipse by itself without any extra defense items, provides enough to increase the active's duration by 1.3 seconds.
Iceborn Gauntlet, while somewhat expensive and uncommon, will allow you to keep targets locked down for much longer due to the slowing field in addition to providing good defensive stats. Though you won't be able to take advantage of the proc as frequently as other champions, the utility it provides may be just enough.
Attack Damage Bruiser
Leona has very high base defense and utility. Using the right build and combination of items, she can dive into the enemy backline and be a major threat to their damage dealers. While being played as a solo laner or jungler, she can use this build to accomplish this. The best choices for this role contain a mix of damage, cooldown reduction and some defenses.
Without a lane partner, Shield of Daybreak becomes Leona's primary ability, as it grants an attack reset, extra damage and a stun.
This combo is especially dangerous from the brush - keep track of her.
Zenith Blade has a small width and slightly short range - staying back or side stepping can help you dodge it.
If Leona uses Zenith Blade to farm minions, it can sometimes be advantageous to make it hit you and force her into a bad position.
Stay mobile in order to make it harder for her to effectively initiate with Solar Flare and her combo.
Spread out to minimize how many people will be hit by the stun from Solar Flare, and possibly the entire ability.
Catch Leona alone whenever possible, as she cannot make use of Sunlight without a teammate.
Any damage from her lane partner will proc Sunlight, notably damage-over-time, greatly increasing damage taken. Try to force her to use most of her skills before her teammate can activate the marks.
Leona is hard to finish off in combat due to the bonus defensive stats from Eclipse. Only commit to killing her if you are sure of victory.
Leona's largest source of personal damage comes from Eclipse, which also provides her the most defense. Try to keep your distance from her when you see her activate it.
It is difficult to disengage from Leona, but if you can dodge another Zenith Blade, which has a small hit area and a notable casting time, you can cripple her ability to chase. Coupled with her low base movement speed, it is possible to escape from her by simply running in a straight line away from her.
When laning, Leona is most effective when she can surprise her foes from the brush; warding your lane's brush can be a very effective way to diminish her zoning ability.
Be careful about using knockback abilities such as Condemn or Buster Shot on Leona when she uses Zenith Blade. If you fire before Leona starts her dash, she will be able to dash to the last enemy champion hit regardless. Instead, try to time the shot to hit just as she starts to dash, which will break her dash and knock her back, effectively canceling her gap closer.
Remember that Zenith Blade places Leona behind her target with respect to her point of view on using Zenith Blade. This can be exploited by knockback abilities to either throw her into one of your turrets, into your team, or to Condemn her into a wall with proper positioning.