In terms of strumming the guitar while palm muting, it can be used to achieve a more driving feel to the song, hence you will hear it being used more often than not in a Rock concert etc.
In my opinion, there are more than enough sites out there attempting to explain how to achieve palm muting. Therefore, I'll be using a picture I found from one of these sites to illustrate how palm muting can be achieved.
The steps you can take to achieve palm muting are:
- Place your hand across the 6 strings as seen in the picture above.
- Focus on the strings that you want to strum (most people won't strum all 6 strings when palm muting). Therefore, it is common to see people using barre/power chords while palm muting. That way, you only have to focus on the bass strings on the guitar to palm mute.
- You can enhance the muted sound by applying pressure on your left hand when hitting the notes, and releasing pressure when you're not hitting the notes.
- As for what angle your pick should be when strumming while palm muting, my general rule is to use it at a 45 degree angle upwards when strumming down, and a 45 degree angle downwards when strumming up. The reason is explain in my "HOW TO hold a pick/plectrum when strumming" post.
I hope this post has answered your questions on how to palm mute. Enjoy.