How do you decide what subject you will shoot? This is where you determine where your interests lie. If you wish only to take pictures of wildlife then you will have to be patient and wait for the subject to come into view. Obviously you can go to a wildlife park such as the Rocky Mountain National Park and hope to find subjects, but if and when you see them will most often it will depend on the time of year. Elk and Deer are more prominent when they come down the mountains to mate and eat. Birds and insects will always be available, but the type of birds and insects will vary based on the time of year. If you are in Alaska chances are you will have several chances of shooting a Bald Eagle, while in Florida you may find herons or cranes.
You will need to select the photography themes that you are shooting depending on the photography skills that you want to practice. A lot of us are relegated to the area around us and are limited in the type of photography that we can practice. Landscape photography requires the use of the land you have around you, and, unless you are going on vacation to some place new, this will limit the type of shot that is available. Your ability to travel will be an important factor in determining your choice of subjects. Do you have to limit your photography to subjects that are near where you live, or are you able to get out and travel throughout your region or even around the world