Although I think it's quite early days for me to thinking about my portfolio, the link above goes into detail on a few key points to consider. I'll summarise them here.
1. Unprofessional communication
How you communicate says as much about you as your art does. It might seem like common sense, but make sure to pay a lot of attention to spelling and grammar when communicating with potential recruiters. Keep your standards high and be concise and efficient but without coming across as self-entitled - "Humility and gratitude create a strong foundation of true relationship. And true relationship is the foundation of true success."
2. Your portfolio doesn't fit the job your applying for
Customise your portfolio to suit what is required of the job you are going for. For example, if you are applying for a storyboarding job, your portfolio should show mostly storyboards with maybe some of your other very best work at the back. Taking the extra time to do research into the position you're applying for, and presenting your work suitably, goes a long way.
3. Ambiguous intent
You should decide where you fit in the industry, not your employer. When asked "What kind of job are you looking for?" avoid saying "Anything." If you're unsure of where you fit in, seek advice - but not in a job application.
4. Unprofessional presentation
(This is probably my biggest issue.)
A portfolio should not show your growth as an artist - it should only show your best work, and reflect your potential as "an artist and human being". If it is unprofessional then you will be unprofessional. Be creative and take the time to make it look its very best.
For Digital Portfolios (Website, iPad, PDF etc.) :
For Physical Portfolios:
5. Too much art
Less is more. If you don't have enough work, get a smaller portfolio (or make more work!). Around twenty five pages is the limit. If you have too much work to show, it will be overwhelming and confusing - it's better not to overstay your welcome.
Chris Oatley has a lot of other articles of this nature on this website (like this) - it's an overall excellent source of advice.
I certainly don't think I have enough work finished to my highest standard to put together a portfolio, and I'd like to avoid filling one up with unfinished and/or mediocre work in the meantime. I'd prefer to put more time into creating good work so that it will reflect me in my best light. I also still really need to work on the presentation of my work - have some sort of logo/signature maybe, and a consistent font to give brief titles on my concept pieces to give some sort of context.
A big focus for me next year will be on making my art appear more neat, presentable and professional.