Build path

Start with energy stream (mana one). If youre ahead go for requiem buy the Braid first then move on to the next item. If behind build crystal tier and skip requiem all together. Tainted totem is most useful if the other support is a healer or if theres a life steal jungle like Kha. Your adc may need atk speed more than healing, in that case Marshal is a good item to pick up.

General Support Tips

Protect your adc and follow what they do. You can lead a horse to water but you cant make an ADC engage so position yourself in front of the adc to be able to follow their flow in a moments notice as well as to take auto attacks that would hit them. Another useful trick is to body block minion last hits. This is most important to do for large minions but is also wildly important right before level ups so you can push a level advantage for early kills (this is for real high level play but good to keep in mind).

Warding

Try to place wards at cross roads
For river wards go a few extra steps to place them, you need time to react to jungles so they cant be too close to lane. As the game progresses youll need to ward important points like fangtooth or orb prime as well as start moving wards to more heavy traffic areas like in front of blue and red to give your team more information
If there is a Kallari then wards in the middle of lanes can be useful to counter