Small tip

You can enhance this mockup by using Shadows Overlays. 

There are some free shadow overlays in this mockup: https://mockups-design.com/free-simple-stationery-mockup/ 

Just copy Shadow Overlays group from "Free_Simple_Stationery_Mockup_1.psd" into this mockup beneath "Contrast" group and start playing with the settings:D

Enjoy!