It's no different than writing a poem, story, or a musical. Most of the work is done in your head, not on paper. A habit I started after high school was to carry a small notebook with me wherever I went. Into this notebook would go the musings and ideas that would at some point provide material for a new project. Today I use a software program called Info Select, into which I copy the scribbles of my notebook.
Web pages are another strong point for the program.
Photo House, Ver. Today, no design program of any quality is complete without photo editing ability to retouch out or enhance items in photos for inclusion in your design. Without this capability your work looks amateurish. This is a professional level program with some special effects brush, drag and drop photographic objects, frames, etc. However, photo editing for expensive color advertising is another matter.