1) If inspiration strikes, run with it. Bob Gale said he was inspired when looking through his father's yearbook, and he noticed his father was class president. Gale wasn't at all friends with his own class president, and he wondered if he would've even been friends with his father if he went to high school with him. (see http://backtothefuture.wikia.com/wiki/Recurring_gags) Obviously the final story really has very little to do with that little snippet, but it seems like some of the most popular stories originate with a simple idea or image. (And most popular stories can be summed up in a sentence or two. Which is hard for someone like me who comes up with complex ideas...)
2) Use cause and effect to build your story. The commentary discussed cause and effect in a simple way I was able to grasp. Basically, they wrote index cards of each scene, and then put them up. They used this to show them what other scenes to add from there. For instance, they knew they wanted Marty to introduce rock and roll to 1955. That meant they had to have an earlier scene in the 1980s to show that he could play guitar, so there's another card. Frankly they made it sound really easy, though I find it really hard to pull off in real life.
I don't know that Scribe Meets World's screenwriting post on the structure of Back to the Future was written in response to the commentary or not, but it seems to have some good stuff.
3) Embrace restrictions; they can actually help you write a better story. If you know much about the history of Back to the Future, you know the original climax was going to be at a nuclear testing site (!!!). This involved more setup in the introduction (to establish when and where the nuclear tests were happening and how they worked) and required the characters to travel some distance prior to the climax. The main reason they had to change it, however, was because they had to cut some money out of the film budget!
In the end, moving the climax to the clock tower in Hill Valley made the film infinitely stronger. I think sometimes when you're faced with restrictions--whether it's Nanowrimo, the restrictions of various Christian or secular publishers, or perhaps even facing feedback from critique partners or editors--sometimes these limitations can lead you to greater ideas.
Of course, I tend towards making too many changes and having too many ideas. If I had been writing the movie, I likely would have come up with several even less plausible ideas and perhaps never even realized the clock tower idea (had I had it) was the golden one!