If there is a .mod (dotmod) file, you can install automatically with ME3Explorer.
You will need:
ME3Explorer. Download it here.
By default files are located in
C:\Program Files (x86)\Origin Games\Mass Effect 3\BIOGame\CookedPCConsole
Back up the PCC files you are replacing.
Replace your default PCC files with the modded ones.
Open ME3Explorer and run TOCBinUpdater.
Click File and Check PCConsoleTOC.bin
Your PCConsoleTOC.bin should be located in:
C:\Program Files (x86)\Origin Games\Mass Effect 3\BIOGame
It should find updates to the changes you've made. Hit yes and a 'done' window should pop up. Close ME3Explorer.
Replace your modded PCC files with your original backups.
Run TOCBinUpdater again.
Infinite loading is a sign of a TOCBin update error.
Sometimes the TOCBin goes wacky and won't work despite being updated with ME3Explorer. Try throwing away your PCConsoleTOC.bin manually, then running "repair install" through Origin to replace it - this will completely revert your game. Then try to install the mod again as normal.
If you can load un-modded saves but modded saves crash to desktop it's likely a Gibbed save error. Make sure there are no extra spaces before or after the codes you have changed.
If you've really broken your game beyond repair, go into Origin and right click Mass Effect 3 for the "repair install" option. This should revert your game to its original state.
Any additional technical problems with ME3Explorer should be directed to the official forums: http://me3explorer.freeforums.org/