How do I sand leather

[Tommy217xxx]

I recently picked up a bench mounted belt sander for cleaning up my work. It seems like I’m making more dust then actually making my work look better. 
 

What grit belt do I use? Also do I apply pressure? I’ve been putting my leather on the table and moving it back and forth. I’ve been working with 3 layers on 2-3oz chrome tan leather.

 

Thanks tj