One of my ideas to get flow going in the writing process is to choose a book I really like in the genre I want to write in. Then I look closely at how the author writes dialog, describes scenery, shows emotion, makes time pass, etc. I choose my own story and copy the techniques of the writer I like. If I'm having to work at getting into the writing process, I can just copy parts of the story I like and experiment with changing a character's reaction, the time of year, or creating a different outcome to a problem. This type of writing practice gets me into the writing without worrying about creating something out of nothing - a problem I can easily have on a day I've been too busy with other time demands or when I'm feeling tired. Once the writing process gets underway, I can tackle my own projects.
Practicing writing in this way isn't much different than the practicing a musician does. Jazz artists spend hours transcribing well-known jazz players' solos to get ideas, rhythms, and immerse themselves in that particular style of playing. The end result is their own solos are richer and have the right sounds and patterns for the jazz idiom they're playing in. Composers spend hours listening to and practicing other musician's compositions. Why shouldn't a writer spend hours reading and practicing the writing techniques of other writers they admire?