Well done for trying. As with all things it takes practice and lots of it. There are many ways of achieving an end result with photoshop. My one tip would be to work with the image magnified as large as possible when you are cloning. Well, actually I do it in stages, do a rough general tidy up first then enlarge, do a bit more, enlarge again, do a bit more...each time reduce the size of the clone brush. Also work on a duplicate layer so that if you do make a mistake you don't lose the original.
Whatever you do don't give up trying.