I don't really need pointers because I know why I'm bad. My biggest problem is that I play way too many champs and roles. So then I never get used to last hitting with them, I never get used to match ups, I never really master anything. I'm fixing that, or at least trying to, by just sticking with Jungle or Support in all my games.
Not only that, but I often play late at night when I'm tired and/or drinking, so my mechanics are usually not crisp, not to say my normal mechanics are anything fantastic.
My positioning is bad because I really like playing bruisers/tanks and when I play a squishy champ I tend to forget I fold like a wet paper bag.
I basically don't concentrate enough while I'm playing. I probably should do that more often.