As someone else mentioned, I avoid anything political unless I'm purposely diving in for entertainment. The tech comments are normally high quality, and tend to force me to think about my opinions. Also, while everywhere has some level of group think, the tech comments tend to be pretty balanced.

I've developed a bit of timer in my head. If I feel like I've perused HN too long or catch myself just refreshing the home page, I close the tab and move on.

Finally, and this isn't HN specific, I never start my day by checking sites. I always do a solid 2-3 hours of work (sometimes 'deep'), before anything else.

EDIT

Other thing, is don't argue on the internet or HN. I'll share my opinion and/or respond a bit, but if someone really wants to argue, I let them have it and move on. Takes too much time, and doesn't gain anything once I'm ok with my position. I mentioned the other day in another HN post that I had stopped going to FB for this exact reason. Zero helpful information, and it just led to arguments which take too much time and accomplish nothing.