Meditation, Visualization, Word Count, Page Count, Timed Writing, Boot Camp, Retreats, Accountability Partners -- all methods of increasing writing productivity, and it seems to me, I've tried them all.
In trying a variety of methods, I am discovering what works and doesn't work for ME as a writer. All reasonable, valid methods, I've learned that each works for some people, but not for all. One might work like gang-busters for an individual writer, while another might be that writer's particular solution.
There's not one way that's THE right way of increasing productivity. There's what works for YOU as an individual, unique writer.
On Author Rachel Aaron's Pretentious Title writing blog, Rachel addresses a way to track and increase daily writing output production. She actually finished a book in 12 days, please see Rachel's 12 days of Glory post! Rachel went from writing 2,000 words per day to 10,000 words per day.
I so appreciate Rachel sharing her system and can vouch to the fact, for me, her method is working! I may not ever get to 10,000 words a day, but I've found what's working to increase my productivity.