Depending on what you play, and what you face.
1.: Protector
: Their primary goal is to protect the ADC. Unless they face another protector poking with them is risky, and against tanky all-in it's a suicide.
for most case, and
if you facing another protector, or you are seriously confident in your skill to dodge everything.
2.: Poker
: They poke the living shit out of you in lane phase. Strongest on lvl1, but if fails to get kills/assist in lane phase, then worthless until lategame.
goes always. As your job is to poke the enemy to death. Also you most likely push while poking which let you attack the enemy turret.
3.: Tanky all-in
: Before lvl2, or 3 these guys are worthless. After that, if they land their skillshot it's over. Assuming they are not half dead already.
goes for them for extra survival. The first part needs a bit of skill, because you don't want to waste it. ALWAYS keep one charge to get cannon minion with it. Some people keep the other charge until healing actually needed. Once upgraded it's best to keep 2. charge for healing, and one charge always goes for the cannon minion. In later stages you just use when you can, because teammates farms the minions before you can.
Beyond these gold items there is no special income. Outside of getting kills/assists of course, and some minions, if your ADC is not on lane. You make up for it in most cases, because the items you need are fairly cheap. Except for poker champions since they use mage items, but as told. If you fail to get early kills/assist with those, then you are fucked until late.
One last tip both for supports, and ADC.
If you face
focus her.
If you face anything else focus the ADC. You are never strong enough to kill the support before it can use it's own skills, and after that it's worthless for a time. The ADC however deals far more damage over time. The support might seems important, because of the burst, but the overall damage in the fight is far less, than the ADC's. In case of protectors the support can protect herself good as he can the ADC unless you face Soraka. And against a tank it should be obvious why you focus the ADC first.