Having your motorcycle setup properly for your size, stature, riding style and skill level can dramatically increase the handling characteristics of a motorcycle so along with routine maintenance, dialing in the optimum setup is something that should be done on a routine basis and considered when going from one track or riding area to another, as well as during changes to weather or conditions of a course.
Having a motorcycle setup improperly for a rider (which is an all too common scene) can make a day at the track, trail or ramps much less enjoyable than what you were anticipating, if not dangerous. It all comes down to having precise motorcycle control in all types of different terrain and conditions.
Having a motorcycle setup properly can mean the difference between "Being along for the ride" or having precise motorcycle control which will enable you to win races or competitions and impress your friends with your mad skills and not leave them laughing about how "Out of Control" you looked.
A log of changes should always be recorded in something such as a laptop computer, spiral bound notebook, or log sheet so you can always refer back to what made a substantial change when returning to a track, trail or riding area.
Considering the countless adjustments that are available on a modern dirt bike such as the very basics of adjustable handle bar mounts, or handlebar and foot operated control positioning to the more advanced setups such as fork leg height, fork offset, externally adjustable high and low speed compression damping, externally adjustable rebound damping, internally adjustable suspension valving, suspension oil tuning such as fork oil height and oil viscosity in the forks or rear shock, and front and rear adjustable spring preloads, all of which changes when combined and tuned properly can make a dirt bike's handling so smooth that the motorcycle just becomes one with a rider, whereas the rider can just flow with the terrain and make the motorcycle react naturally to a riders inputs, versus constantly fighting the bike.
Elsewhere on this site, you'll find many topics that you should find useful and should get your dirt bike setup for your riding style and ergonomics, just remember, a lot of these changes are not "set and forget", as a lot of these adjustments and especially sag should be checked constantly and "clickers" should be fine tuned when going from one track or riding area to another or even to stay on top of changing conditions such as mud, sand or ruts.
With the aforementioned info in mind, just review the links below and pick the type of riding that you are most involved with, whether it be Motocross, Off-Road disciplines such as GNCC Racing, Enduro's, Hare Scrambles or Trail Riding or FMX, but first review the topic of "Basic Motorcycle Controls Setup for the Individual Rider" and "Establishing the Baseline Settings and Setting the Sag" to ensure your basic dirt bike setup is ideal for your size and riding style.