Some people email me to ask if they can second shoot for me and when I ask them if I can see their work, they don’t really have anything prepared.
It is VERY important for a photographer to have a portfolio of your own work because this shows people your photography level and skill.
Make sure your photos are technically decent. Meaning, no blurry photos, no snapshots, make sure you edit your photos in Photoshop to make them the best photos they can be.
Try to keep only your best photos in your portfolio. On the other hand, don’t be so paralyzed by not having great photos that you don’t include any photos at all.
ONLINE PORTFOLIO
At first, it doesn’t have to be anything fancy. You can create an account in the many photography sites for free. Personally I prefer Flickr. See my portfolio there at http://www.flickr.com/photos/silvasphoto/.
Some people use their myspace or facebook account as their portfolio.
You can also use a blog such as WordPress. Just make sure you can post BIG photos. See my other blog at http://SilvasPhoto.wordpress.com .
The good thing about this is that you can just give people a link and they can view a lot of photos. This is better than emailing photos because you are limited by the no. of attachments allowed by your email (which is probably around 3-10 depending on your email provider.)
Note about emailing photos: if you absolutely have to email photos, make sure they are resized to a smaller size otherwise, when the person opens the photo, it will be too big for the browser and there is no way to view the whole photo unless you save it on the computer, then open it with a photo viewer, which most don’t people don’t like to do.
Eventually your goal is to have your own website that showcases your work.
Things to remember:

PRINTED PORTFOLIO
When meeting people in person, you’d want to bring a printed portfolio. The photos in your portfolio should be in a big size, such as 8×10 or larger.
You should select a number of your photos to include in your portfolio. 15-20 images is a good number. The portfolio that you present should be relevant to the job you are applying for. Example: if you want to be a portrait photographer, your portfolio should have portraits. If you want to be a landscape photographer, you should have some landscape photos.
I have different portfolios depending on the client that I am talking to. I have a wedding portfolio, a portrait portfolio, a landscape portfolio and a boudoir photography portfolio. Now, I don’t want to show somebody who’s not really interested in landscapes some landscape photos since that is not relevant to them.