The Summoner's Guidebook: I suck at middle lane in LoL

There are five roles on Summoner's Rift, and I play four with reasonable competency. Support is my strongest role; I'm cautious and attentive and I like warding. Also, I don't have to last-hit, a role at which I feel my skills are a bit deficient compared to the rest of my skillset. Despite feeling deficient at last-hitting, though, I actually play carry fairly well, given my current matchmaking rating. I am virtually always ahead in creep score compared to my opponents, and if an ally in my lane gives up first blood, it is almost always my jungler grasping at an opportunity that is not there.