Look for poles that have a telescopic adjustment. Poles that telescope offer several key benefits. First, multiple people can use the same set of poles simply by adjusting the length. If you are going on a long downhill segment of a trail, you can adjust the poles to be longer and take a lot of the strain off of your knees. Likewise when you are climbing uphill you can shorten the poles and gain more power with each step.
Some poles practically collapse, much like an antenna on a portable radio.
These poles are ideal if you don't plan to use them all the time and want to stow them in your pack, safely out of the way. Look for poles with anatomic, soft grips. Grips that have been shaped to fit in your hand comfortably and have some give will be easier to use for a long period of time. Grips that are hard can get wet with sweat and can be uncomfortable to hold. If the grip doesn't fit your hand properly move on to another model or see if they can be changed out.