Students work on a larger paper in stages (proposal with sources, outline, first draft, final draft). This succeeds particularly well with stronger students who already understand some things about writing. They are more likely to take the process approach seriously from the start and they will think about the earlier stages of their work. Be sure to build in peer and/or professor review at each stage.
Some students think that all they really have to do is write the final draft¹. You can get them engaged in the process by grading each stage as a separate project or by assigning a hefty percentage of the final paper grade to each portion.
¹These students may write the final draft, but it will probably not be any good since they have not actually participated in any improvement process along the way.