The best advice I have heard regarding improving your photo taking skills it to take LOTS of photos. Makes sense, everything you do a lot of you will normally get good at. However, once you start taking lots of photos you quickly realize that you now need to organize LOTS of photos. Last year I took just over 10000 photos, which is a lot of organizing. This is where Adobe Lightroom comes in. It is considered my many to be one of the best photo organizing and editing tools for photographers. It doesn't come cheap, at $300 but if you are going to only buy one piece of software to edit your photos this would be the one to get. It took me a while to learn because there are a lot of options but once you figure it out, it is amazing!
For those who don't want to shell out the $300 (and I can't blame you), before using Lightroom I was using Picasa from Google to organize and make small edits to my photos, it works great for a free program but can't really compare to the features in Lightroom.
Every photo I have take goes into Lightroom because it is my photo catalog but I also use the editing features on most photos as well, here are the ones I have posted that have had some editing done in Lightroom.