One of the downsides in having a very active community, is that there are too many new threads and comment showing up in the Recent Content or Popular content areas. There is a way to limit what you see if you don't follow one of the Categories or Sub-Categories.
Define the Categories that are important
The 1st part of this is customizing Your View to show only the Categories/Sub-Categories or Groups that you want to follow.
Just navigate to the Categories/Sub-Categories and click Follow this community (see yellow highlighted area under the Actions menu).
Customize Your View
The 2nd part of this is customizing Your View to only show the things you are following.
Here are the steps: