d7000 help to improve bird photos

That's what I think needs to be done, get closer which I have in some instances, but I don't get consistent sharpness. I do get some that I find acceptable but I also miss quite a bit too, I know the lens is not great for this (nikon 70-300 at 300). The thing that gets me is I set the shutter to only release on focus and assume that would mean the objects will be in focus especially when moving side to side.