LF Advice From A High Elo Support Main

I'm currently plat 1 and main Thresh. I haven't been playing soloq as much as i used to and i want to start playing more again. I would normally play Thresh or Blitzcrank, these are my best supports however I want to start playing other champs like lulu janna etc. My question is when should i pick a certain support with a team. For example we have a tank top and jungle already should i go a healing support. I really have no idea when to pick which support. https://euw.op.gg/summoner/userName=Korean%20Carry
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