Sheryl shared this insightful piece on modeling the writing process...
When I was first told to "model" for students, I was terrified! I didn't want them to see that their teacher wasn't perfect at everything she does! :-) BUT, I soon realized how great it really is for students, and now I actually enjoy doing it.
This year, I got the most effort/product out of my students' writing AFTER they saw me struggle and "mess up" in front of them. When they realized that this is something that can only improve with practice and that even your TEACHER has a hard time thinking of things, they respond so well.
I find that they often try to help me come up with things to write--they want to help write my paper. When it comes to writing their own, they think about the help they gave me, and try to apply it to their own work.
I also think students have to see that writing does not start out perfect--they need to see the cross outs, the rewrites, the spelling mistakes, all of that. When they realize that it's OK to make mistakes intially, they have an easier time getting their thoughts down.
It doesn't always work, obviously, but it does more good than bad.