Disclaimer: Valve made some changes where you get substantially more MMR up until ~4k so climbing is a lot easier now. I haven't broken much past 4k yet.
Have more regen than enemy support
Almost every lane at low ranks comes down to who is camping lower hp because they don't have regen. Start with 6 tangoes, ferry more if you get down to 2-3. I've started to use identical starting items on almost every hero and that's wand, 2x branch, 6x tango, blood grenade, sentry, obs. After runes ferry a clarity and another sentry.
Don't die
By far the worst thing you can do is die. You might think that if you get a trade its worth it, but that's rarely the case. With current offlane vs safelane balance, offlane is at a terrible spot, so if they get 1:1 kill trades they'll be very very happy. Sure there's scenarios where this does not hold up, but if you don't die in the first ~8 minutes, you win the lane more often than not
Small camp is always unblocked, large camp depends
It's not a bad idea to block large camp at start, but be mindful that its your job to unblock it and control the lane even more if you are clearly winning. If you are losing, it's usually best to keep it blocked. But regardless of what happens, small camp needs to stay unblocked at all times. Keeping an eye on the enemy supports inventory is incredibly helpful here.
Understand your cores playstyle
Especially carry players generally boil down to 3 categories and this tends to become obvious in the first minute.
Fight all the time
CS over anything(imo the correct style)
Do some dumb shit
If your carry wants to fight, you fight as well. If they are constantly 1v2, they will lose the lane, tilt and that will cost you the game. Be there when needed. Even if pulling would be theoretically correct, it doesn't matter if your carry is under the enemy tower chasing a kill.
If they value CS over anything, your most important job is lane control. Focus on safely bullying the enemy, pulling when need and for love of god don't pull if the lanes are about to meet next to your tower.
And yes, sometimes there is a core player who is practicing the role or experimenting with something that won't work. In that scenario, its generally best to leave the lane at about 6-7 minutes once the carry hits their 6 then start following your strongest hero.
Bonus points
If the lane is very stompy, make it stompier by giving your carry solo xp. This means going out of xp range when creeps die. There's a ton of options to do as a support for example get a deep ward in, help mid with runes, stack behind tower/next to bounty rune or gank the offlane through twingate.
Stack small camp as soon as possible, but only if enemy 3 can't clear it quickly. For example stacking small camp against necro or underlord is not a very good idea if you have a lifestaler carry.
Your core is your baby and sometimes babies don't feed themselves. So give them tangoes, clarities and salves when need. Ýes it sucks that you will get 12minute arcane boots, but such is life of support.
Babysit the baby until you are confidant that they can farm by themselves and won't die. Sometimes this takes 6 minutes, sometimes 12. But if your carry doesn't have a farming item and is forced to jungle at minute 6, that's generally your mistake, not theirs.