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-mate to last-hit large waves, especially if they have AoE skills.
Beware casting Zenith Blade near enemy towers; you can be pulled under the tower and take aggro.
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.
If Leona's lane-mate is fed enough, and/or her laning partner is a good 1 v 2 champion (like Urgot), she can begin roaming as soon as she purchases movement speed and at least 1 (if not 2) gold generating items.
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 power, 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 attack, and immediately issue an attack command afterwards.
Leona is described as a "pure tank", favoring builds that only emphasize her defensive stats.
Despite the fact that all of Leona's abilities scale with ability power, it is not suggested to build AP as she has low AP ratios and long cooldowns.
However, due to the fact that all of her abilities including her passive deal magical damage AND she tends to be in the center of the battle, Abyssal Scepter is an acceptable choice.
In between her cooldowns, Leona can be quite vulnerable early game and your opponents may decide to focus you down (especially when Zenith Blade often puts you behind enemy lines). Consider getting Sunfire Cape early to make your enemies think twice about coming near you. It gives a nice chunk of defense and also helps with farming/pushing.
If you have Randuin's Omen, try to use its active ability while Eclipse is up. Randuin's Omen's active increases in duration the higher your armor and magic resist is which Eclipse provides (the total armor and magic resist are taken into account).
It is recommended to build as much cooldown reduction as possible without hindering her survival items. The more CDR she has, the more she can spam her CC and tank for her team to clean up. Remember that the cap is 40% CDR.
Since Eclipse provides Leona a high amount of armor and magic resist, even with no items, she will, generally, gain more of a survivability boost from items, runes and masteries which provide bonus health as opposed to more armor or magic resist.
Leona's effectiveness is heavily based on her ability to position herself correctly in team fights. Runes, masteries, spells and items which improve her mobility and/or increase her resistance to slows, stuns, etc. should be considered especially useful.
This combo is especially dangerous from brush - keep track of her.
Zenith Blade hits a rather small area - staying at range will allow you to dodge it.
If Leona uses Zenith Blade to farm minions, it can sometimes be advantageous to make it hit you - without her combo lined up, she doesn't hit too hard.
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 Sunlight deal damage without a partner.
Any damage from her lane partner will proc Sunlight, greatly increasing damage taken. Avoid her partner's attacks, especially Damage over Time effects.
Leona is hard to finish off in combat due to to bonus defensive stats of 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 once you do Zenith Blade may be a fantastic gap closer, but the projectile speed and cast animation are slow enough that it makes it hard for Leona to effectively chase with it. Coupled with her low base movespeed, it is quite possible to escape Leona simply by running in a straight line away from her.
While 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 shut down 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 knocked back only 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.