Are you absolutely sure that the reason your shot isn't sharp is misfocus? It could be motion blur from too slow a shutter speed. A
lot of beginners really overestimate how slow they can go, and how much help stabilization like VR/IS can give them in their 18-55 kit lens, and they have horrible handholding technique.
Personally, I often get better accuracy with autofocus than I do with manually focusing, since today's dSLRs are designed for autofocus and don't give you manual focus aids like the old film cameras used to. I mostly use one shot autofocus mode and the single center AF point.
Articles you might want to look at are: