I found out very early on that you needed a couple of things when assigning projects for grades that were open to interpretation: clear expectations AND examples. Without one or the other, you risk being disappointed when students turn in their work. One way I have been able to combat that is by having a clear rubric with clear assessment guidelines.
If you head over to The Organized Classroom Blog, you can pick up your free copy of my rubric (which you can type right onto!) and see a few website resources that will help you to set your clear guidelines for grading as well. Next time you assign a project, you will know what to expect on turn-in day. :)