21 in Utility is a must for supports, with the bonus starting gold you can start regen pendant with a ward for a fast philo stone, you only need to save up 360 gold which is easily done and then some. Should be able to get philo and another ward by the time your ward is dead.

Clairvoyance is still a viable and great spell for supports, I take it on all of my supports because even though it has been nerfed, it is still a free ward for a short period of time. Heal I haven't been a big fan of until using it with Leona, perfect for baiting bot lane into ganks from your jungler or even in just a 2v2 fight.

Support your lane, be aggressive if you have room to, passive if you are losing the lane. Junglers are your best friend and you can help set up ganks very nicely, especially after you hit lvl 6. In team fights you want to stun their bruisers who are focusing your carries, this is done easily with the q, but you can also use her ultimate for this. Her w makes her very durable to take a lot of damage in lane and team fights so it should be up whenever its off cooldown for team fights.

Leona probably has the best ultimate in the game when it comes to a support. The range is ridiculous, it activates fast, and its an aoe stun/slow. Sets up ganks really well and stops people from easy get-a-ways.