Help undercutting my M&P

[oldschool88]

So I finally decided I want to try undercutting the trigger guard on my M&P and I need some advice. Does anyone have any reccomendations on how to go about it? I have tried to find a video of how to do it but have had no luck. I also want to notch the part of the trigger guard where my reaction hand goes. I have a file and sandpaper that should work, but I would like some input before I just start hacking at it... Thanks!

[The Virus]

dremel and sandpaper