Ask colleagues, bosses, clients and vendors -- people you work or have worked with -- to write a recommendation for you. If it's someone you'd love a recommendation from, but you've lost touch, find them on LinkedIn, write a recommendation about their work, and they may just reciprocate. If not, ask them to.
Take time to fill in all of the options. If you use Facebook and Twitter professionally, add those links. If you have a website, include a link. You can even go a step further to include links to your favorite books, especially those that may be impressive in your field of interest. All of this takes time and thought, which is well worth the effort to present your professional best.
Be thorough about your experience. LinkedIn says user profiles are 12 times more likely to be viewed by recruiters for potential opportunities if you have more than one position listed. While it's much faster to list only one job -- your current or most recent position -- by investing the time and effort to fully develop your profile with your previous roles, it will pay off.
Finally, get involved. LinkedIn is most effective when you're actively engaged in the network. Join GROUPS connected to your interests, your places (or former places) of employment, and desired industry. (I have my own group with 23,000 members that you're welcome to join.)
Use ANSWERS, which is a feature that allows anyone to ask and/or answer questions in a slew of categories. This is a smart place to showcase your expertise. One great answer won't win you a job offer, but a pattern of expertise will most definitely catch attention.
Follow COMPANIES that you're targeting to work for. You'll be able to easily see when someone joins a company, leaves the company, or moves into a new role, as well as receive headlines on company news.
As with all online social networks, the more active you are and the more people you engage with, the more success you'll have. Just signing up -- and then abandoning your profile -- isn't likely to do much for your career. Get involved to make good things happen.