Here's some of the control and adjustment options:
The first thing is where to put the handlebars: back or forward. Also the position in the clamp... there's many possibilities but here, my preference is to line up the handlebars with the forks, not too far forward nor too far back. You may want to adjust this and move forward or back if you cannot comfortably have a proper Standing position. See Positioning the handlebars in the supports for details.
The rise is important. To adjust the rise, there are all kinds of after-market risers you can buy. Why you'd do this is to get a comfortable standing position, where you don't have to reach too far, or too low and still be able to keep the elbows up.
You may need between 0 and 50 mm of rise, and it's a function of the shape of the bike and your body. What I suggest is to get a kit of swappable risers if possible, which allows you to rise in steps and test them untill happy.
There are also special anti-vibration risers, but these are most likely overkill for most dirt bikes - you should look at them if you have a big single-cylinder dual purpose bike.
Wide bars make for easy handling but tree-banging, so, if you think they're too wide, you could cut them. That could involve changing the clutch-side grip though. See more below.
The forks can be adjusted up/down in the triple clamp. This not only changes a little bit the height but, more importantly, it will change the rake (the angle of the forks with the ground) which massively impacts the handling of the bike. Raising the forks a mere 4 mm will change the rake by 1 degree and alter the steering dramatically.
The steeper the forks, the twitchier the bike is: it turns very quickly but it is less stable at high speeds. Look at bycicles for that - most have the forks almost vertical and are very twitchy.
If you lower the forks too much, then the rake gets more like that of a cruiser and the bike is harder to turn, but more stable at high speeds.
As with every adjustment, it is best to start where the factory setings are and play with it while paying attention to the changes in behavior.
If you don't like the behavior of your bike, this is one of the things to look at - the rake angle. Certain lower links require adjustments in the rake angle and/or fork position.
There are bikes with special rake adjustments - we won't discuss these, but now you know what that's for.
At least, you should check the torque on the all the bolts there: handlebar bolts, triple clamp etc. I have seen brand new bikes with loose bolts! Open the owner's manual and get used to a torque wrench - it's useful.
One thing to worry about when adjusting the handlebars is make sure the cables and wires are fine, especially the throttle cables: move the handlebars all the way left/right and make sure there is no change in RPM...
If you re-arrange the controls, make sure the kill switch is handy - you may have to use it with the clutch pulled in or a finger still on the brakes for instance, so make sure it's within easy reach. Make sure to read about Adjusting the levers for a dirt bike.
One way to break your wrists is from having the bark-busters set too high and, when landing or hitting something head on, your wrists slide under the guards and... well, painful things occur.
Make sure your bark-busters are set low enough to prevent that situation: when your wrists slide off the grips, they can stop in the busters or slide over their top.
This is especially important with the metal-backed bark busters.
Things to look at when selecting handlebars is not just the color and reviews, but also the rise and shape, make sure it fits the clamps you got there, as well as the stuff you have, like bark busters, switches and mirrors.
In terms of comort, the rise and bend are relevant. These are not easy to figure out so I normally stay with whatever type of handlebar is OEM for the bike.
The length of the bars is also relevant. You will see the more expensive are already marked for cutting at the edges. A wide handlebar will make for easy handling of the bike but will get you either stuck between tight trees or thrown off the bike in tight woods: they tend to hit trees.
It's hard to give you specific advice here. At the very least, make sure you can fit all the equipment you have on there, before cutting it.
Next, continue reading about grips and vibration++.
Other dirt bike setup topics:
More stuff to read / watch related to dirt bike handlebars and setup: