Stop copying and pasting your art into mockup frames! There's a much better, non-destructive way: Smart Objects.
When you buy a good mockup, the template is often set up with a Smart Object layer. It usually says "Place Your Design Here."
- Double-click the thumbnail of that Smart Object layer. It will open in a new tab (.psb file).
- Place your artwork into this new tab. Resize it to fit perfectly.
- Save this .psb file (Ctrl/Cmd + S).
- Close the tab and go back to your mockup file.
Boom. Your art is now perfectly placed inside the frame, with all the angles, shadows, and textures of the mockup automatically applied. Need to swap the art? Just repeat the process.
This is THE professional workflow for mockups. Are you using Smart Objects yet?