Find student portfolio examples by searching online, reading professional development books for teachers and consulting colleagues. At Scholastic, you can view sample portfolio items from expert teachers. Nancy Atwell's book In the Middle is another excellent source for viewing sample forms for student portfolios that are focused on writing.
For specific advice and real-world examples, a good place to turn is fellow colleagues. If you are a student-teacher or online teacher looking for colleagues to support you, try contacting local schools to find a mentor teacher. You can also join your field's professional organization to network and share teaching resources.