This is not my original idea, but from author Theodore Sturgeon, who spoke at a writing conference I attended circa 1983 — I never forgot the story.
Theodore received a frantic phone call from the wife of a writer he knew. She explained he was suicidal and stuck on page 20 of a screenplay for an hour long drama (normally 45 pages) and had a deadline looming and was paralized.
Theodore asked "does he know how it ends?" "yes" she said. Theodore told her "okay, tell him to take page 20 out of the typewriter, and insert a fresh page. Number that page 25, and continue from that point. Come back and work on the missing, "stuck" section after getting through to the end."
That is the best practical advice I have ever heard on the subject. Today, with typewriters ancient history, I'm pretty liberal about skipping around. If I'm stuck on a section, I simply insert a row of Xes: XXXXXX as a marker to come back to later.
When working on screeplays, it's fairly easy in that the writing is broken up into very definate scenes. But it works for other writing as well. I've found sometimes the part i was stuck on was more because I was forcing it in at the wrong point, and the exposition I was trying to force came out naturally later.