Firstly, who do you main support as?
I'm a low elo support, but usually it goes like this:
Support the ADC
ADCs start trading
If win: Continue to farm/push lane to deny enemy team (Do not attack minions as support unless your ADC isn't there) minions and shave health of tower.
Once the enemy pops back, poke them as much as you can get away with
Once out of mana, b
(Usually if ADC overstays I will tell them "lets b" or "going b, be careful")
if lose: punish the winner as much as possible, back up behind tower, b
I'm assuming you're just backing up because "Ooh I have enough gold for boots" or whatever. Don't do that.
Good luck summoner!
edit: I should say if you win the trade super early, wait until ADC has enough for a BF sword or whatever; don't just instant b because levels > gold/items (generally)
Kinda a hard question to answer tbh but that's the jist