What is some good advice to help people who are training for a 5K?

Regular Massage Therapy will keep your muscles properly relaxed and able to meet the demand you put upon them with training and actually running the distance. It's better than stretching which I strongly discourage before an athletic event because you train to build your muscles strength and much like a rubber band if you stretch the muscle out is looses it's explosive ability to kick it into high gear. Warm up and cool down yes. Stretch muscles to relax it and keep it's power with warming up!

Gradually increase your mileage until you can do the 5K in its entirety.