This is simply the build that I use when I play Leona, so far it works great for me, friends of mine who tried it also say that it works for them too, which is why I decided to post it here. Leona is a great champion, I enjoy playing her each time, hope everyone else would find this build working for them as it works for me.
Some might say that I should build her more on Defense or Utility, but believe me from my personal experience Leona like this not only is a tank but is a killer as well, I managed to be able to actually kill enemy champions specially using the Solar Flare.
What is important to know about this Leona build is that it is a strong burst, and with good team it is almost unbeatable, again from my personal experience. The skill rotation is simple, before you attack you use the Eclipse and then Shield of Daybreak, immediately after that you use the Zenith Blade. So what happens now, when you dash to the enemy champion with the Zenith Blade you stun him/her with the Shield of Daybreak and when the Eclipse explodes it prolongs the stun from the Shield for 3 more seconds and plus it deals magic damage, they will not really die from all of this that is why you finish them with the Solar Flare. The beauty of all this is that you do aoe damage with all the skills except the Shield of Daybreak, but that is not much of a trouble because you will do this action only if you have at least one more champion with you on your side.
So, in short here is the rotation of the skills:
All in all you can both tank and do high damage like this, which is more than helpful for your team.
Optional item for this build in early game is Malady
, it gives attack speed and AP and most important it reduces enemy's magic resistance by 6 for 8 seconds and it stacks 4 times, plus your basic attacks deal 20 bonus magic damage, which for early game kills is fantastic.