What do you want?
If there is one thing to take away from all my film classes are one fact-what ever story that you want to make into a film (or in a still) you must keep one thing in mind: why are you making this and why do people care to watch it? The best part of the whole prone t is coming up with an initial idea and fully running with it leaving no stone unturned. This is really one one favorite parts is the research. There is nothing better than an individual(s) who are fully educated in all parts of the subject matter they are writing about. Research is fun, can be time consuming, but in the end that is by far that will make your story, real and factual.
Research does not stop there. research types of movies which have well written scripts and characteristics you want to see in yours, link them to your bookmark page, watch them, twice or more and if you really feel connected to it, try watching it with no sound, see if it changes for you. Also a good tip is to rewrite your favorite one and see what pattern it creates for you and tweak it. Research the editing techniques to- those are not learned over night and some can be time consuming and difficult to do, so one must also research that (and practice).
Once your research is done- start jotting down all the details that come to mind, do not leave any ideas out- if you do you are doing yourself injustice. Remember the key- beginning, middle and end and stay true to what your point was...why do people want to see this?
Once you start doing this - WRITE.
There are plenty of software out there but the best I feel is a template that you form for your needs, create your own personalized template, but retain and follow those software fields. Include all and any details that you want to see, hear and feelings and emotions that you war to create for your audience.