At my local parkrun, once per month, they have "pacers" . Usually starting at 20 minutes, they go to 40 minutes in 2.5 minute increments.
I am finding that a good "strategy" to use at parkrun is to use my 5K PB as a guide to your current level of fitness and input it into this calculator goodrunguide.co.uk/Training... From this I use the TEMPO pace recommended to run my parkruns each week. In the early days, I would simply run 1K intervals at that pace with a minutes walk inbetween - now I run the full 5K at Tempo pace.
THEN - once per month (and once per month ONLY) , I use the pacers to allow me to see how fast I can go. This way , if I follow ( say) the 30 minute pacer, and if I can keep with him/her, then I know I will do the 5K in 30 minutes -- if I can do that, then next month I will do it again or I will track the faster pacer (knowing that I probably can't keep up with him/her - but as long as I don't fall behind the 30 minute pacer I know that I am somewhere between 30-32.5 minutes for the 5K.
I do see people trying to break PB's EVERY month - and I am convinced it is part of the cause for the injuries that I also see