*** Drink coffee (caffeine). It is a legal sporting stimulant that used to be banned. Go figure! If you weigh 68 kg you require 2 mg caffeine per kg body weight for a 2 hour event (sorry not 5k). You take 136 mg once an hour before competing. One espresso is about 100mg. Or try a Red Bull energy shot (also contains tuarine but I think may now be discontinued). Caffeine has as many PROVEN benefits as all the illegal stimulants you may or may not have heard of BUT the effects and side effects of caffeine are known and understood and legal. Other caffeine-taking protocols will have you taking, say, 200mg of caffeine 5 mins before a race. (Look at the High5 energy sachets, for example, or their excellent race-nutrition web site which funnily enough recommends their products)
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 : https://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.