Advertises for some pay methods, but also has advice on free writing productivity schemes. The focus is more on novels (like Rain in the Mountains director Joel is writing), but could apply as easily to screenplays.
It’s my experience that even buying a bad screenwriting how-to book can be good motivation to write. The best thing to do is to not postpone writing when inspiration strikes: Paul Schrader reputedly wrote Taxi Driver in 48 hours. The next best thing is to find a workable routine and be consistent: Stephen King doesn’t do anything else with his day until he’s written five pages. Most days, this doesn’t take him long.
Oh, and Stephen King — he has a how-to-write book too.