There are some new hiccups with rooting so don't just jump in without reading first. The newest Evos are coming with some changes to the hardware and the bootloader so you have to know what you have and choose the right root method.
This is what you need to know, hardware version, hboot version, and software version number. You can find 2 of these in the phone menu/settings and the other you'll have to enter the bootloader to find.
First, go to menu/settings /about phone and select hardware info, at the top will be hardware version.
Second, hit the back key, and then select software info, on the 5th line it will have the software number.
Next power down your phone by holding the power button and selecting power off. Then when phone shuts down, while continuing to hold the volume down button press the power button, the phone will enter the bootloader and on the second line will say HBOOT with a number, this number is very important for which root method.
If your software version is 3.29### or lower and you don't have HBOOT 2.02 you can use unrevoked at
unrevoked. This is one of the easiest methods to root.
If you have software version 3.30.651.# or HBOOT 2.02 unrevoked will not work and you will have to use this method:
[ROOT][GUIDE] HBoot 2.02 S-OFF - Like a Boss Edition! - Updated 11/20/10 - xda-developers