Be very careful if coming down.
Holbert Trail starts off relatively flat and is wide and smooth. After crossing a couple sandy washes, you'll come to a paved road where you'll turn to the right and follow the signs to continue up Holbert. This is where the trail becomes very rocky and technical, with large rock all over, making it fairly slow going as you must be extremely careful in your foot placement.
You'll go through many switchbacks and several spots where the trail appears to split. Follow the signage, and you'll be fine. Near the top, you'll cross pavement 1-2 more times before the trail ends at the intersection with the National Trail
I encourage you to take the National Trail
to another trail (Kiwanis or Ranger) to go back down. Holbert is very technical and difficult on the way down. It makes for a very scary run down on Holbert.
There is a turn off to go to Dobbins Lookout about 1/2-3/4 of the way up, which can be an excellent spot to admire the view and catch your breath.
Lots of cactus. Snakes in certain parts of the year.