Neep help properly masking parts when making user skins

I’m trying to get into making user skins and I’m using photoshop. I’m masking out things piece by piece so I can actually then texture those specific parts. My masking is really bad though. The following is me trying it on the Mirage 2000 C S4:

This is not good masking. I know it’s not good masking. But I don’t know what techniques I am supposed to do to actually get better. Tips?