I don’t have a lot of feeds and I don’t even use categories, labels, etc.
I have some filters which are designed to mark as read articles that are sponsored (i.e. ads) based on keywords in the titles.
In a typical day I’m always in All Articles and simply keep an eye on the articles coming in; marking as read things I know I’m not interested in. When I have free time, I glance through All Articles and read the ones that are interesting.
There are some times when there’s a tech conference (CES, for example) which usually means a lot of sites are publishing similar content. Those days I actually click into individual feeds to read the articles that the site in question is good at covering (Apple-centric sites for Apple stuff, Windows-centric sites for Microsoft stuff, etc.).
If I had 300 some odd feeds I’d probably operate in a similar manner but use scoring to push up/down articles based on keywords.
As fox mentioned, there’s no real right or wrong way to use the software. It has plenty of options to suit a variety of use-cases. Experiment and find the way that works best for you.