This is a fix I made on a "medium grade" rug, made with rows of stitching. Nicer plush rugs may not work for this.
It also helps if the rug is a little multicolored to help hide your repairs.
I'll go over a small and large snag, with photos. I already just about finished the large one when I decided to document it.
Flexible fabric glue (I opted for some that dries clear and flexible)
Straight pins (or something similar, for the large pulls that yield long pieces of string/yarn/fiber)
Scotch tape (as needed)
Something heavy like a text book
Step 1: Trim
Step 2: Glue
Use the tip of the glue pen or your finger to work the snag into the hole.
If possible, work the surrounding fibers into the hole to help cover it and look more full.
Step 3: Set
My glue stated 2-4 hours dry time, so I just left it over night.
Now for the large snag...