I once read a description of purgatory as like floating deep in a cold sea, and every time you moved, spiny, sharp toothed, ugly deep sea fish spotted you and came for a nibble.
That's what LinkedIn used to be like. If you moved, some guy would try to sell you something.
It's really, really not like that any more. People are actually loving it.
So don't make the mistake of only making connections on LinkedIn when you need something.
Build your network beforehand, so when you need them, they're there for you.
Check LinkedIn every day, and as you meet new people, connect with them there.
Get it done by: http://linkedinfluence.com/
For: .. I recommend this course