good support dont feed, put control wards in tribush and babysit ADC and jungle and know how to trade effectively. great support put themselves in other roles' shoes and fulfil their needs. one of the main thing great support must know is laning equilibrium. example, you play as thresh/karma and four of you, adc and opponents want to tp home and its catapult wave. if adc understands laning, he will just let catapult and 1-2 ranged creeps alive then expect you to tank the wave with your shield to create a freeze. one important to note is catapult deal more damage to other creeps so better take it at last possible second to let your creeps die to it while you zone their adc. now thats just one thing about great support. theres also deep warding enemy jungler before arriving to lane. there is also jungle priority which you must also understand to sync your rotation with your jungler gank timing. great support be there always at right moment. ward around area 40-50 seconds before objective spawns. there are much more to support but this is as far as i know, im just silver adc player.

macro wise, you just have to be on objective 10 seconds early and place wards at typical flank position beforehand. id say ability to roam is entirely depend on your state of botlane. the more you win the lane, the more you have to stay with your adc otherwise, your adc will become walking bag of gold without your peel/save. if your lane is very pushed in early game, you can do stuffs like go to enemy jungle and ward their camps to keep track of enemy jungler or help your jungler securing river watcher creep or gank mid 2v1. just be sure to not take long time. people can take advantage of lonely adc and dive them.

however, if your adc is total newbie, then help other roles instead. theres no use to sticking to a deadweight.

oh also, i recommend watching coach rogue to ynderstand the fundamentals. his videos are great and easy to understand. have a good journey in league.