The setup of basic motorcycle controls on a dirt bike such as the handlebar position, clutch and front brake lever positions, as well as the shifter and rear brake pedal positions, along with the other motorcycle controls discussed below can make a rider much more fluid on a dirt bike resulting in smoother riding and faster lap times, or a greater ability to throw hits higher and further with confidence, so this is certainly an area to give attention towards before you just start twisting clickers and making other suspension adjustments or modifications searching for that perfect feel.
Also, (where applicable) some of the motorcycle controls discussed here may also be discussed elsewhere on this website in the articles about specific riding disciplines. An example of this that you may find would be in the off-road setup section where the issue of cutting handlebars to narrow their width, or cutting grips for use of handguards will be discussed.

If you already have a set of handlebars on your dirt bike that you seem to have
a liking for, but you're open to trying to get them to fit you a little
better try this:
If you do find yourself looking for a different set of handlebars because the
handlebars don't fit so well, or they're bent
and you're famous for having yard sales, you may want to consider upgrading to a stronger set of handlebars, or a clamp and bar combo as there are many choices available that are seemingly indestructible and offer greater ranges of adjustability than what's generally obtainable using OEM clamps and conventional bars.
Once you have picked out the best handlebars and / or they are positioned in the most optimum setting, be sure to tighten the clamps securely (tightening the most forward bolts first), then be sure to adjust the other handlebar mounted motorcycle controls as discussed below.

As for adjustments to the throttle for an individual rider, there really aren't any, except for maybe the amount of free play in the throttle before opening of the throttle valve or raising of the slide.
To obtain the proper amount of play in your throttle, you want to first ensure that it closes properly when released as detailed in the article on ensuring your throttle returns to closed properly, then adjust the cable at the throttle housing, or at the carburetor (throttle body on fuel injected bikes) so there is approximately 1/8" of free play in the grip before cable pull is felt, as this will make the bike feel less twitchy overall.

There are a wide selection of available grips to choose from and they come in many different compounds, colors and styles, so you may want to experiment with different compounds and styles to find a grip that suits you or your rider best before settling on any one grip style or compound.
Once you have found a handlebar grip that suits you or your rider well, you may want to review the article on handlebar grip replacement so the grips will stay secure on the handlebars because there really is nothing more annoying than grips that twist all over the handlebars, not to mention the safety hazard associated with this if they are so loose that they could come off the end of the handlebars.

Just remember, if an engine stop button is positioned in a way that it is facing you and you're riding aggressively, sudden and unintentional application of the engine stop button is entirely possible with either your knee, wrist or thumb so for these reasons, it IS best to position the engine stop button so it's facing in more of an upward direction, and away from a riders wrist area, as an aggressive rider making contact with an engine stop button is how these are sometimes accidentally applied, and people find themselves taking a trip over the bars.
One other thing about the engine stop
button that needs mentioning while on the topic, is to ensure that the
electrical lead(s) and connection(s) leading to the engine stop button
are securely routed in a way that they are not struck by the triple
clamp, or fork leg when at "full lock" in one direction, as well as not
being pulled when the handlebars are at an opposite "full lock"
position, as either of these scenarios could possibly interrupt the
spark suddenly, or cause the engine stop button to stop working, neither
of which are any good and are easily avoided with proper routing as illustrated in a factory service manual specific to the motorcycle being serviced.

Generally (as a starting point) It's best to position the levers at an angle where they can be easily reached and operated while sitting or standing, and in the attack position, as well as a relaxed position and the best way to obtain this setting is to leave the lever perches slightly loose, then ride the dirt bike, and while riding change the position of the levers until finding the spot that feels best, then return to the pits, (or truck) and tighten the perches securely so they don't slip.
Finding the sweet spot for your levers may take some time and experimentation but there are also a few things to be aware of...
In addition to the vertical placement of the clutch or brake levers, there are levers, perches or lever and perch assemblies available which offer adjustable lever reach settings for even further fine tuning of a riders lever positioning. Before you start purchasing levers though, be advised that there are perch assemblies or clamps alone available with an insert which will enable the lever and perch to rotate in the event of a crash, as well as there are folding levers or lever and perch assemblies to consider which will allow the lever to pivot so as to prevent a broken lever, perch or master cylinder so these are also a choice to consider and there are several quality levers, perches and rotator clamps to choose from here. You do crash don't you?
Additionally, the lever and perch assembly offered by Works Connection has a nylon
insert so the perch can be tightened securely, yet still rotate should you get all swapped out and auger the bars into the ground, and for those with a four stroke, the Works Connection lever and perch assembly comes complete with a "hot start" lever built in to the clutch perch, so consider this when shopping for replacement lever and perch assemblies.

If you're planning on riding freestyle motocross (FMX) and doing flip and trick variations, you may want to consider a set of superflips so as to prevent yourself from losing the bike, or going over the bars while performing flip variations or other combos.

If you're serious about tailoring the dirt bike to
fit you or your rider in the most ideal way possible, picking up a gripper seat or seat cover and foam is a very good idea.
If you are taller than average or have problems when transitioning from sitting to standing, you may want to consider adding foam to the seat to raise the height of the seat, which in turn raises your overall height on the dirt bike and conversely, if you are vertically challenged, or shorter than average with problems reaching the foot pegs or worse... The ground, you may want to consider trimming some of the foam off the seat to be able to obtain a lower seat height.
Additionally, If you are going to be working on hucking massive gaps and doing trick variations, you may want to shave your seat foam so as to prevent your boots from getting hung on the seat and causing any problems.
Be aware that if you do make changes to the seat height by either removing or adding foam, it will likely be necessary to reposition and adjust the other motorcycle controls such as your handlebars and lever positions as discussed above.
Lastly, the trick thing to do if the seat is already at the correct height is to remove the seat cover and using additional foam, build up a "hump" on the seat just behind where the rider normally sits, as this adds a point for the rider to "push against" and it serves as a reference point for the rider to know where he / she is at on the dirt bike, yet this does not generally hinder a riders ability to get back on the seat if the rear wheel is suddenly kicked up. As a reminder, the "hump" can and should be added to the seat if the cover is off and you are customizing the height of the seat for any purpose other than clearance while performing freestyle motocross trick variations.

Aftermarket Foot Pegs are an excellent upgrade and this is especially true for stock pegs that the teeth are dull on or even worse, foot pegs that are old school and narrow,
combined with being dull and possibly even pointing down at the ends. If what you're standing on is the OEM peg and it's worn out, or the teeth are dull, the foot pegs should be replaced and upgraded to a better quality unit, as the foot pegs are what provides you with secure footing and they are an important part of your motorcycle's controls that is customizable.

Getting the shifter positioned properly is critical and luckily for us this is fairly easy to do.
In addition to the fact that there are shift levers with off-set tips and varying lengths, the shifter is mounted on a shaft with many small, fine pitch splines and
can be removed and moved up or down one spline at a time so as to reach
just the right position. A good starting position for the shift lever is
so that the bottom of the shift lever is level with the top of the foot
peg, then adjust the shifter in increments of one spline position from
there to reach the perfect spot, where you can shift effortlessly while
sitting or standing.

Similarly to what was just mentioned about the shifter, you want to position the rear brake pedal so that the top of the brake pedal is level with the top of the foot peg as a starting point, then adjust from there.
Fortunately, the rear brake pedal is one of the foot operated motorcycle controls that is used frequently and is much more finely adjustable than that of the shifter, as the rear brake pedal has a clevis with a threaded rod that can be adjusted in very small amounts, or it can also be adjusted so as to make a drastic change to the brake pedal position if desired so be sure to spend some time getting the rear brake height set just right.