As Dave said, the focus is already perfect. The blurring is only due to the rapid motion of the wings (and also the feet).
It's a bit under-exposed, which is a common problem when shooting into a bright sky. But as Dave said, it's usually better to under-expose than over-expose; you can "rescue" a slightly under-exposed shot.
To avoid motion blur, it's very important to use the fastest shutter speed possible. That means using the best lens you can afford, and the fastest ISO that won't turn your photo too grainy.
The other thing you can do is anticipate where the bird is likely to be and place yourself accordingly, so your back is to the light (hint: do your shooting in the early morning or late afternoon, you'll find more birds that way anyway) and you have a fairly clean and dark background at some distance behind the bird. Try to get up at least as high as the bird, for a more intimate and unusual perspective. If you can manage such an "ambush" type setup, you can also bring an external flash to bear, though that may bother the birds and may be illegal in some cases.
Obviously, a lot of the best pics of small birds are taken at or near feeders or baths, where the bird's perches and flight path can be easily predicted. Getting a decent flight shot is otherwise a matter of great patience. I've got some in-flight shots of gulls, geese, herons, and tubenoses, but for smaller birds, almost none.