This is more advice for AD carries than it is for supports, but the support should be positioning similarly to the AD, so I'm including it in this series.
The question is, if you're not actively last-hitting a creep, where should you be standing in lane?
What I notice a lot of people do, especially in replays that I watch in the 1100-1300 Elo range, is, when they're not actively taking a last-hit, to back off completely. This doesn't seem like a problem until the enemy starts to take advantage of it. When you back off, you're letting them walk up without forcing them to deal damage to you and thus draw minion aggro (you would be damaging them too, but since they're the ones aggressing, they would be taking the bulk of the minion damage). In other words, you're letting yourselves get zoned.
Why is this such a big problem? Because it's much easier to hold a dominant lane position than it is to gain one. If you're trying to walk forward up to someone who's actively zoning you, they know exactly where you're about to walk. This lets them better aim their own skillshots and dodge yours. If he has a pink (which he should), their support can gain control of a bush that's usually out of their influence range had you started out near your creeps. And if you can't win a trade that might turn into an all-in, you can't walk back up to them at all.
The advantages that superior positioning give pile up, and you find yourself falling behind in experience. Once you're a lower level than your opponents, it's even harder to gain on them because you can't trade autoattacks evenly. This isn't so much of a problem if you're playing a hypercarry and just want to farm for lategame with it being ok to be 30-40 cs behind at the end of laning, and sometimes it's unavoidable if you're unable to exchange and they can force you to back off from the creep line---remember, being dead gets you the same amount of experience as being in base or being zoned, and being in base or zoned doesn't give the enemy carry 300 gold.
That brings me to the other point, which is that if you're behind already, there's no reason to fight for the ability to stand within experience range of creeps that aren't dying. Don't give up your positioning for free, but if you are unable to maintain your positioning for some reason, there's no reason to fight their zoning until you actually need a lasthit or just the experience of a creep dying.
It takes a lot of practice and experience to learn when you need to back off, but if you start to position more aggressively when there's no pressure on you, you'll find that a lot of the time you're able to force your opponents to back off when they don't have creeps to farm and then keep them pushed away even when they do.
Next time will actually be the post about teamfighting; I just wanted to do this one because it's something that comes up in a lot of the replays that I watch.