I work from original photographs ONLY!!! I use both my traditonal 35 mm AND digital pocket camera. I have boxes of prints categorized (roughly) and since I work in both graphite and watercolor - find this to be my most valuable resource. I look for abstract or dramatic light and dark patterns - and geometric shapes/forms for most of my work. I work very realisticaly - doing watercolor landscape/buildings and trees/rocks in pencil. I start with value sketches - done on a light box to save time. I simply put tracing paper on my photos and look for interesting value patterns and contrast that I establish with B grade pencils. It is a time saver.
I work exclusively in the studio as I do very detailed works - and do not have the time to work on site.
If I get blocked or do not know what to start on next - I look at these value sketches/read art magazines - ( I have a huge collection from
The Artists Magazine)or go to a different medium ( I also do jewelry) I also use my collection of watercolor books ( especially the Splash series from North Light Books) to get our of a slump when I am looking for an idea. I also do artist trading cards - it makes you think differently when you have to change the scale you are working in!
Sometimes doing exercises from those 'creativity' books helps also.
I would suggest that your art students keep a camera with them at all imes - you never know when you will see a dramatic subject...and it is so easy now to print out works.