Google has stated their goal of providing only useful sites in your search results. They just made a major change that affects about 10% of everyones searches. But until they make search perfect, they also created an extension to their Chrome browser that lets you personally blacklist any site you don’t want to see again. When you blacklist a site, the site address is also sent to Google for research on improving their results.
For Chrome only, you can install the extension by visiting here: https://chrome.google.com/webstore/detail/nolijncfnkgaikbjbdaogikpmpbdcdef