A modern creative needs to be a constant, calculating, self-promoting machine. Working in your basement on projects that never see the light of day may be personally fulfilling, but doing so rarely gains you work or recognition. How, then, do you start sharing your work? Some suggestions:

Make a portfolio / blog / microsite that acts as a showcase for your work.
Make sure the site is easy to update and expand, in respect to the point below.
Keep that site constantly updated
If nothing new has been posted over the last six months, people assume (rightly or wrongly) that you have been out of work for half a year. When you do find yourself in need of work, the last thing you want is to spend three weeks trying to bring the site back up to speed before you can do interviews.
Create a stand-alone copy of the portfolio on a mobile device (smartphone, iPad, etc - anything that you have always on hand).
You should be able to show what you do anywhere, to anyone, at any time. Sometimes it will be when you are in a ski lodge on the side of a mountain at 5000 ft. elevation with no WiFi or cell signal.
Share both completed work and, if possible, works-in-progress (WIP).
Showcasing completed work is good, but showing process is even better. People are fascinated by construction; it also allows potential employers and clients to see how you work. Some creatives are concerned that this "gives away the farm": the truth is, I can watch an oil painter work on canvas for hours; it doesn’t mean that I will be able to do anything she does. But I can appreciate and admire the process.
Share work and experiences outside your immediate interests.
Rarefied skills are good, and desired. But well-rounded people fit better into teams. Show that you are more than a mere creative unit: bring as much as possible from your life into your art. Share your influences, passions, and sources of inspiration. Baked a particularly nice cake? Take a advertising-quality photo of it.
Cross-promote your work on social networks (Facebook, Twitter, LinkedIn).
Not everyone is going to visit your site. Keep everyone updated, and interested, by using social media services.
Contribute your work and feedback to relevant communities. (flickr, forrst, deviantArt, CGTalk, Behance etc)
Find forums, critique sites, and industry gatherings that reflect your interests. Contribute your thoughts and expertise. Develop both the community and your personal reputation at the same time.