I never force it. That's why I always carry a pad and pen with me in my pocket just in case words hit me right then. To me, it's always spontanious. I can't just sit down and say I'm going to write something for someone or about something that I've experienced; I wait 'til it comes natural.
Now, if you're talking about writing a report for school and it has a due date, I feel for you, man! That's hard!