Set Up Your Account ASAP!
This will obviously only apply to some people, but if you haven't already got a LinkedIn profile, then get one. They're free (unless you want a Premium account) and easy to set up, so there's no need to put it off any longer. The sooner you set up an account, the sooner you'll potentially appear on recruiters' radars when they're looking to fill a new job.
And, of course, creating a profile immediately gives you a better chance of building up those all-important contacts - do you know someone who knows someone who's looking for someone like you?
Sell yourself
How you word this depends on whether you've already got a job, but either way it's important to present yourself in the most employable light.
If you've got a job, then don't mention anything about seeking "new responsibilities" or wanting to take the "next step in your career", but if you're unemployed, then run wild and sell yourself in the best way you can.
Be professional at all times, but also keep it brief and engaging - basically, treat it as a mini CV. Recruiters are only likely to scan your LinkedIn profile, so give them details of your key experiences and attributes straight away.
Look smart
Unlike with your CV, a photo is a necessity on LinkedIn and could make or break your profile, so keep it professional. There's no reason to put on a suit and iron your shirt, but use a photo that at least makes you look presentable (anything drunken needs to be left purely to the realms of Facebook).
A simple photo of you looking relatively smart and smiling should do the trick.
Think About Keywords
As mentioned above, recruiters will look through many, many candidates and are only likely to skim your profile so, to make it easier on them, try inserting a few keywords that show off your best skills.
Often, recruiters will search through the entire database of profiles on LinkedIn by using a location and a relevant keyword or two, so if you've neglected to use a couple of vital words on your personal description, then how do you expect to stand out among the millions of others?
Change Your URL
Sometimes in life it's wise to be a geek - and this is one of those occasions. By changing the URL of your profile from something like www.linkedin.com/pub/tomdavis/60/8c34/768 to www.linkedin.com/pub/tom_davis, you'll make your LinkedIn address look much smarter and also demonstrate that you've shown attention to detail. And employers like that kind of thing.
It's free, easy to do (just go to the ‘Edit Profile' page) and takes a matter of seconds.
Get Some Recommendations
Possibly the best way to make yourself stand out from the hoards of other job seekers on LinkedIn is to gain some recommendations. These are simple to get hold of - just ask your current or ex boss or one of your colleagues for a sentence or so, and consider writing one back too if it's appropriate.
It's worth remembering though that one or two well-written recommendations from respected people within an industry can count for a lot more than a stream of single line reviews from your work mates.