You may have already read my discussion already about picking a role. Naturally I was thinking about it a bit today. If you've picked a role, for crying out loud be good at it. Nothing is more irritating to me than getting into a game where someone firstpicks a role and then plays awfully. Examples include picking any last-hitting lane role and being bad at last-hitting, picking support and being passive in lane, or picking jungle and not exerting map presence via wards, ganks, counterganks or invasions. It might also be picking mid/top and getting wrecked by any matchup you're not familiar with.
I recently played a game where my team's Vayne was forced into ADC. She really wanted a solo lane, but both of them were picked by an obvious duo queue. The duo queue went on to play terribly. Katarina let the enemy Vel'Koz free farm while she attempted to put pressure on bottom lane, while our Jax lost horribly to the enemy Teemo. I couldn't gank top past level 6 (you can't really gank a Teemo lane) so I ended up playing proxy mid and jungle invasion because my mid laner was rarely in her lane. I would like to emphasize that Shyvana versus Vel'Koz is not a very fun matchup.
Likewise, our Vayne was garbage and would not ever shoot at the enemy. I understand being defensive and all, but I don't think she understands the need for ADC to continuously shoot. Our support would make plays but she wouldn't follow up, and unless Kat was around, basically nothing would happen.
Now I understand that you don't always get the role you want, but screwing someone who can play the lane out of the matchup so that you can lose your lane or give your opponent free farm is not really OK. Yes, I do think that ganking is important for a mid, but you really need to push up and ideally harass your opponent out of lane or kill him before you gank. I'm not a pro mid player, but you generally rotate as mid when you're ahead, not when you feel like giving the enemy hits on your tower.
What I'm saying, and what numerous games where this happened (I had jungle stolen from me by the worst Evelynn ever) have told me is that you really need to know your role. I mean really. Pick a role and actually learn what the heck you're doing. If you don't know what you're doing in a role, don't call it until you know!
Maybe I should just have talked about the skills you actually need to have to do well in a position. I dunno.
Sorry for the meh update (and slow update too), not really feelin it today I guess?