You asked about the sky- honestly it'd be tough to do a whole lot with it in basic. You could try some curves measurement, by selecting portions of the curve to alter based on the tonality in the image. Advanced you could edit the sky separately and do more, depending upon what your original looked like.
One other thing that might have added to the sky is if you underexposed the whole scene a bit to keep more detail in the sky and not blow it out, and then tonemap it afterward. I've found you can bring a lot of dark shadows back successfully in this manner, and since you underexposed you'll be pulling more detail back into the highlights in the sky. It sorta works better on some images than others, but definitely something to consider.
Sorry about first comment and the low first rate. I just misunderstood rules of the contest about having or not peoples in the frame...Anyway I will fix my mistake. Thanks for you understanding