One thing which helped a lot was realizing just how slow things really move. People post very interesting technical things every day, but those are usually the products of maybe a year of intensive offline effort. You don't fall behind by skipping reading those. You do fall behind by endlessly reading those and doing nothing with your own time. Four hours sitting with a textbook in your area of interest is worth more than a month's worth of twitter posts. As a corrolary, you needn't worry about falling behind in general - because of how slow things move, you'll always be able to catch up. It takes probably two orders of magnitude less effort to understand a concept than to research & come up with it in the first place.
As you develop an area of interest and talk with other practitioners, you'll naturally hear about interesting things eventually. The rest is just brain candy you wouldn't have cared about anyway.
The only thing I find unique to Hacker News is much higher quality analytical comments about politics, economics and tech industry labor issues. Almost everything else is in one ear out the other.