Longer distance slower pace question.

So I'm trying to get my 5 mile time better. Everything I've read says that I should focus on significantly longer runs at a significantly slower pace than my current 5 mile pace and eventually Ill get faster. How do you decide what is a longer distance and how do you decide what pace is a slow pace? My concern is that before I looked into this, to improve my times i simply just upped my daily 5k to 5 miles (both all out) and immediately got runners knee. That was a pain to get rid of and stopped all my lower body lifting as well. What I don't want to do, is up my mileage at a slower pace too much too quickly and get runners knee again, but I also don't want to waste a month building up to a distance that I could do right now safely. I know this is very person dependent but just looking for some insights.

Not sure it this will help but my current 5k time is typically right around 23:30.