Still use Reddit but more productively? Also goes for Youtube, etc

My dilemma is this:

I know I waste too much time browsing Reddit or YouTube aimlessly. I don't want to stop the sites all together as I do enjoy certain aspects like thought-provoking discussion and I learn quite a bit from them at times. So I don't want to delete my accounts all together. But I also need to stop the mindless browsing. What's the best way to reconcile the two?

I've thought about not allowing myself to post/comment unless I'm trying to learn something, I've thought about restricting myself to only 30 min to an hour a day, etc. Just looking for some advice. Has anyone found a reliable way to utilize these sites while "trimming the fat" so to speak?