Initially CV sites, spam it out. Then linkedin-there are millions of recruiters on there it's crazy, feels like my network is over 50% recruiters. The more you connect the more jobs you will get spammed, then just set up filters on your email, ignore most things select what you want. Some websites like indeed.co.uk let you filter for contract work.

Add your profile to decent job sites, HN jobs, stackoverflow etc. Make sure you have an attractive profile or cv. Once you get a contract or connect with recruiters it's pretty easy the jobs just come to you. As you build a real network over the years friends and ex contacts can help.