Also, no matter what cutting tool you use, make sure it is SHARP.
I learned how tough feathers are to cut through when I needed to trim some butt fluff off a hen. I had my "good sharp scissors" and thought they'd be equal to the job. No, not really.
This. Exactly.
And this too.
This is a good idea.
If one of your birds should die from injury/sickness, save the carcass to practice on so you can learn how hard you will need to squeeze. No worries about the bird suffering, it can be just "a learning experience."