This entry is for improving your artistic eye. Setting up a shot is half the battle and being able to objectively picture what would make a good photograph is a super important skill. (It's nice to be able to subjectively imagine what would make a good photograph, but I'm going for universal appeal for now.) It's also useful when you're picking out what photographs to display--you want people to see your best work!
My biggest tip for learning how to set up and judge shots: look at other people's work. As in, a lot. Go to photography exhibits. Get out the National Geographic or coffee table books (or whatever prints photographs of the genre you most enjoy) and page through it. You don't want to copy or steal from them, but it will help you decide what you like and don't like. Next, figure out why you like what you do like and why you don't like what you don't like. Is it the angles? The subjects? Look at your own pictures as well. Make a list of things you like, things you dislike, things you did right, and things you did wrong (drawing from both your own work and the work of others). And then set out to work on each skill. Practice each thing individually. You discovered that you like 3/4 view portraits? Okay, go take a TON of 3/4 view portraits (and then re-examine them when you're done to keep tweaking). You also like shots where the person is only half smiling? Okay, on a different occasion, hone that skill. You can put them together afterward, but work individually first.
Judging your own photographs after you've taken them is hard. Having a personal investment can really mess with your objectivity. This goes double if the pictures are of people/places/things that you love. You have to decide whether that photo is wonderful because it's well set up and artistic or if it's because you love the people in it and the memories that go with it. It helps to have other people judge your work on occasions like these but if you can learn to do so it will be invaluable. I suggest picking about ten pictures that you like and then have other people look through them and choose what they like and why (a good way to do this is through facebook). Seeing what they like in your photography is a good way to know what you've gotten right and this is a nice way, as well, to see if your opinions overlap with those of the general public.
Most of all, just practice and look. Go through your pictures after you've taken them. Practice things you like and don't like. And most of all, enjoy yourself.