Practice
A portfolio that tells the story of your work.
From context to outcome: give each project a useful role in your portfolio.
Select rather than collect
Start with two or three projects that demonstrate different skills. Explain why you chose them. A portfolio should help someone understand your work, not simply show that you have been busy.
Make your role clear
For each project, describe the initial problem, constraints and your personal contribution. Distinguish your work from the team's. Show the decisions you made and the tangible things you produced: a document, interface, prototype or presentation.
Document what changed
Finish with the outcome and what you learned. Use numbers only when they can be verified. User feedback, a resolved issue or progress between versions can also provide useful evidence. Update the page as the work evolves.