Are you a fairly new runner? I had terrible runners knee on the left for my first few years running, made most runs pretty miserable but I was stubborn and never took any time off. Then that knee gradually got better and then the other one started up. Handled it the same way, that is to say I didn’t do anything about it and it never actually sidelined me.
Then magically over the last two years it kind of went away. I know this isn’t good advice, but I never stretched, never strengthened, just kept running. I personally feel that my knees just needed time to adapt to being a “runner”, and now they don’t bother me at all.
I Think that it’s often the classic too hard/too fast/too long kind of thing too. embraced the whole easy days=easy thing also. I know you’re not supposed to run through pain, but just keeping running actually worked for me. Now that I’ve been a runner for six years consistently I feel like my knees have adapted. Runners knee gone.
Stretching, strengthening, icing etc may certainly help but consistent training actually did the trick in my case.