It really isn't worth the effort. You need to manually unlike each page individually. There is no way to unsubscribe from multiple sources individually.

Once you have unsubscribed, your newsfeed will be wonderfully straightforward. After a few days it will be cluttered with sponsored likes. I assume this is however long the batch process takes to catch up.

I only go on Facebook to respond to invites at this point. I stopped going on because their mobile app is literally the worst software I've ever installed on my phone though. It's huge and bloated, and it doesn't even include messaging, which they broke out to another app for god-knows-what reason.