The John Muir Laws blog features lots of educational resources about nature journaling and sketching in a variety of mediums, intermixed with conservation information. Also offers resources for educators.
Some of the good stuff (a sample, there’s too much to link, the whole blog archive is a treasure trove)
5 minute landscape in watercolor pencil
How to draw: birds mammals plants
Step by step: watercolor iris in colored pencil, northern parula with watercolor
Read Nature journaling and conservation via MetaFilter
An interesting link found among my daily reading