The command to start exmh looks like this:
exmh -display hostname:0 &
If your DISPLAY environment variable is set up properly,
then you need not use -display, and the command is even
simpler. You don't need to specify a -geometry argument,
although exmh supports one. Instead, simply position and
size the window using your window manager. When exmh quits,
it saves the geometry information of all its top-level windows, so
you can adjust their positions once and forget about them.
You can add the exmh command to your startup X environment by editing your startup file (like .xsession). You might also want to add it to the main menu of your window manager. The details about this vary from X system to X system, so ask your local X guru for help. exmh also supports the window manager session protocol, which means that session-smart window managers automatically start exmh for you.