Picture 1) You were shooting into the sun... sometimes this can't be helped but you need to learn how to keep from having too much light hit your lens. I see you were using a D40 and I bet it was with the kit lens since it was shot at 39mm... you can get a lens hood for your lens that will help, and barring that you can also take a bit of cardboard and shield your lens against the sun. However, this angle will always pretty well be blown out so it is best to avoid it when you can. As far as the subject matter goes, what is it that made you want to take this picture? was it the people, the bench, the trees? Whatever it was could be brought out more.
2) I agree with Rachelsne
3) Good start here on this one... I would advise you to look into getting a polarizing filter, which will really make the sky pop! You can fix that in post processing a bit if you know how... I personally would crop out some foreground because the grass really isn't the focus of the picture.
Keep at it, you are off to a good start.