Firstly, what is LinkedIn?
Well, essentially it’s a networking site just like Facebook… only corporate-y. Instead of all your personal information, it’s basically like having an online resume, and instead of friends, you have ‘connections’. These connections are basically your employers (both past and present), colleagues, and lets be honest, you’re probably going to have your friends on there too. Personally, I think it’s an excellent way to stalk people you know (like Facebook), but on LinkedIn, you might just get the opportunity to exploit your connections to get a job. People post their work updates, and you never know, someone you went to high school with might end up working at your dream company before you, and they might be in a position to help you get a job. Even saying you know someone at the company in your cover letter can be beneficial.
What should you be posting?
Past and present work is a yes, your education is also a yes, but anything from your personal life is big a no-no. Anything rude or inappropriate, also a no-no. It might seem funny at the time, but probably won’t be when your boss and/or potential future employer sees it (and then they won’t even be a potential future employer anymore).
Who should you be adding?
If you’re on good terms with your past employers and old colleagues, you should add them as they’ll be valuable references. Potential employers will then see who you know, what they do, and they can contact them. Which is also why you should only add people you a) actually know; and b) want being contacted by potential employers. You don’t want to add someone who you don’t like, or who doesn’t like you, because you might end up missing out on a fabulous opportunity because of a bad reference.