I agree with what people have told you; Linkedin is a great resource.
My main tips are:
Pump up your profile. Keep it filled with as much as you can. Don't put crap in there, but the more quality info you can slot in, the better. Also, even though there are resume-esque sections of the profile, add personality where you can. Give people an idea of who you are, not just what you've done.
Don't be shy about asking friends to introduce you to other people they know who look interesting. If you see your friend knows a developer who looks really cool, ask if they can briefly introduce you/connect you to them.
Join groups that you're interested in. The benefits of this are three-fold. 1. It helps people looking at your profile learn more about you and your interests. 2. You can learn from the groups, and 3. contributing can increase your visibility and ability to meet interesting people who you would want to connect with.
Have a good profile picture. The more professional the profile looks, the better.
If you have other forms of social media which offer more insight into your strengths, say a blog or a relevant twitter: link to it.
And as other people said, don't be shy about connecting with people you meet in real life, and if you do, make sure to follow up with a message so they don't become a random contact you added that one time.
Happy Linkedin'ing