Color studies
While I have always been drawing, 2010 was roughly the year I seriously got into digital artworks. It really took a leap forward after I started the "sessions": daily photo studies focused mostly on the colours. I must have done about 600 in the span of 3 years.
I spend 15 minutes on each, and color pick afterward to understand where my analyse went wrong. I consider vital to perpetually study from nature and from photos.