*** Use a running track and spikes rather than a parkrun and trainers. A running track, other things being equal, will give you a PB perhaps 20 seconds faster than a parkrun, possibly considerably more (depending on the parkrun). Just a thought.
All the suggestions are starred:
*** 3 stars. IMHO it will work
** 2 stars. It might work
* 1 star. Can’t hurt
X 1 cross. It CAN hurt if done wrong.
All 50 tips are shown here as a series of posts : http://the5krunner.com/tag/how-to-get-a-5k-pb/ or on twitter using #howtogeta5kpb. They are all SHORT-TERM tips that will work in the next week or so with varying degrees of success.