Document EVERYTHING. Work in progress, scribbles, sketches, your process. Not just the finished object. Design is a journey and sometimes being able to demonstrate HOW you got to a particular solution is more important that the solution itself–especially when shopping your portfolio to prospective employers.
Showing up with an electronic file full of pretty renderings and finished models is unimpressive without including the steps involved to reach that final form. Anyone can parade a snazzy picture around and make all sorts of claims as to authorship and their involvement, but without the proof of your work–your ‘sweat-equity’–your A+ doodle is worthless in the business world.