My top three tips:
1. PLEASE fill out your profile. Seriously. Unless you don’t want anyone to know anything about you. This is how you can be found via search. This is how some people will decide if they want to talk to you further. Don’t just include this job, include previous ones. Include things you did, like on a resume, but you have more room.
2. Select a custom profile address. Get rid of http://www.linkedin.com/in/ajkfaklswhatever and put your name in there.
3. Join a couple groups related to your areas of expertise. Even if you never interact with them on the discussion boards doing so gives you the ability to Inmail and see the profiles of the other group members, dramatically increasing your network with just a few clicks.

I’m a little surprised at the advice to have multiple profiles for different activities. I’m curious as to the rationale. You can have multiple current positions and can explain your focus in the introduction area. I would think in an environment like LinkedIn it would be confusing to not be transparent.