I think your off to great start and what I really like, is that you made a great tutorial! It was well presented and I like that you covered all aspects including Tools and Tool shortcuts. Kudos!
There are some problems with the actual composite. The first is that you have four different components that comprise the composite and all four have different light source origins. The most obvious would be the main subject.
The main subject does not blend well and looks pasted on. The skulls are fake looking compared the rest of the image and they look pasted on because they don't blend well with the rock surface they're sitting on. They need some shadows.
Overall you have great techniques, you just need to put more consideration into your composition and work on matching light sources and blending. I feel like you may have rushed this composite for the video tutorial.