1. Open Image using Photoshop (depending on your system may take 15-30 s)
   
2. Press Alt+T - C (Camera Raw Filter) - may take 10-15s
   
3. Set the grain on Effects tab to 13
   
   
4. press OK, then save image. Done!

Adding grain to digital photography, often done to mimic the look of film, can enhance texture, add depth, and evoke a sense of nostalgia or authenticity, making images feel more organic and less "digital" -- in short it's for Aesthetic Appeal.

i find grain is more effective if your image has a plain background, muted color, or monochromes.
here's a comparison of nograin:

and wigh grain:

(you may need to click the full image)

• You can set the shortcut for camera raw filter (Edit-Keyboard Shortcuts) -- recommended since the tool is very useful.
  
  
• My grain value is 13, but you can of course adjust it higher or lower depending on your image resolution. Usually value between 12-15 is enough, but feel free to experiment and share in comments below.
  
• You can further adjust the grain using the drop down triangle on the right side.
  
  
  

my photoshop doesn't have Camera raw filter, what should i do?
i would recommend you update it, i think it's a feature introduced starting photoshop cc, but if you can't/ don't want to, you can use this guide:
https://www.tourboxtech.com/en/news/how-to-add-grain-in-photoshop.html

help, i don't have photoshop!
you can use this guide and implement it to your software of choice
https://www.tourboxtech.com/en/news/how-to-add-grain-in-photoshop.html
goodluck!


Think this tips is lacking impact? want to focus on your character more?
How about adding vignette effect:
guide link

if you want to read more tips:
https://steamproxy-script.pipiskins.com/groups/SAtips/discussions/1/