Sore knee- what should I do?

I started running again in August, mostly on the pavements around the streets where I live. I realise that this is not the best of surfaces to be training on. I started noticing a twinge in one of my knees a couple of weeks ago, and it was aggravated when I did my first race in 4 years, a 6k.

It's not a severe pain, sort of a dull ache. It's worst if I've been sitting for a while and get up. Also, walking down stairs is very uncomfortable. I feel it at the back of my knee and on the knee cap.
Besides the obvious, resting the knee a bit, and finding a better surface to run on, I suspect I need to do some exercises to strengthen my quads and hamstrings.

I would be grateful for any advice, because I really enjoy running now!

Moomoo, google patellofemoral pain and see if your knee symptoms are similar.

Kneecap pain can be maltracking, so might need to work on balancing the action of the quads. In an ideal world the medial quad (medialis) should fire slightly before the bigger vastus lateralis on the outside of the thigh.

Exercises such as straight leg raises, adductor work and squats / lungers will strengthen the necessary areas.

I'm no expert, but this sounds very familiar to my knees - not so much the position of the pain, but the worsening of symptoms when going downstairs and after sitting for a while.

Have a read of this

Hope that helps!