Though most play differently.... playing "well" as a support is subjective to many things.
1st, theres vision. Id suggest that earlier on you max out the control wards you can carry and keep the yellow trinket a little longer until you are out of laning phase.
2nd, it depends on playstyle and knowing how to utilize different champions strengths and knowing their weaknesses (of adc as well). For example, Blitzcrank just is not a poking champ. You pull, you knock, if your adc is a caitlyn then you pull into a trap.... if your adc is vayne you pull near a wall.... etc. Being a good support with him is keeping vision up, pulling the enemy in good fights, getting kills, being able to predict an opponents movements so that you can pull. Morgana is different..... being a goof support with her specifically is being able to predict movements so you can bind people, having good reaction times on your black shield (preferably good enough that you shield AFTER the enemy uses the cc, but BEFORE it hits.... but that takes a lot of practice.) Etc....
3rd, knowing when to roam and when to not and keeping an eye on the minimap so that you know where the enemy jungler is and ping it. If it is an eve, a trick that can be utilized for blue side especially is the ghost poro. Putting it in tribush will cause it to careful ping when invisible eve goes through the bush. You can have the second bit of the domination tree being either ulti cooldown reduce, move speed increase, or item cooldown reduce depending on how you play as well.