Make a list of your expectations for the project. If you are assigning a research paper, your expectations might include a table of contents, an introduction, a bibliography, footnotes and other content-specific requirements.
Describe the characteristics that would fully meet each expectation. For example, a bibliography would be formatted according to the style set for the assignment and would include a specified number of sources. Ideal use of footnotes would clearly indicate what source the student is using for his information.
Assign a number of points to the assignment and then divide those points among the categories of expectations that you've listed. If a perfect score for a research paper's bibliography is 5 points for 10 sources, decide on the number of points that five sources will be worth and how many points one source is worth. Complete the same task for each expectation you've set forth, with a sliding scale of points for each category.
Tally up the total number of points and include that value, as well as the description of the project in your syllabus for the class. This will make it clear to students what your expectations are for the project and how important the project is to their overall grade.