How can I root my LG Optimus M? How can I root my LG Optimus M MS690 on Metro PCS? I've tried Gingerbreak, Superoneclick, and z4root without luck.
I am not 100% that this is for your device, I can't find anything on the LG Optimus SH, these instructions are for the LG Optimus S (LS670)

Requirements  


Download and install the .net Framework. Part of this utility software is needed by the rooting application. Get the .net Framework here.
The rooting application will also need the Visual C++ 2008 Redistribute Package. You can get this here.  
This process will need a Windows PC which runs either Windows Vista or Windows 7.
It is also best to have a fully charged battery before you perform this process.


Instructions  


Download the rooting application from here.
Unzip the downloaded file to have access to the main rooting application.
Download and install the USB driver for the device from here. If you have successfully connected the device to your PC before, you don’t need to do this.
Enable USB debugging in the Optimus S. To do this, just follow this path Settings > Applications > Development and check the box for USB Debugging.
Connect the device to your PC via USB cable.
Open the notifications window on the device and make sure “USB debugging connected” is listed under “Ongoing”.
Go to the folder where you unzipped the rooting files. Right click on “Gingersnap.exe” and then choose “Run as administrator”.
Click on the Root button to complete the rooting process. And, if you just came back here to Unroot the Optimus S, then feel free to click the Unroot button.