If you've only just started using Photoshop, it's pretty tricky to try and explain, but it might be a good project for you to learn how Photoshop works.
I use LOTS of layers in my mockups. This allows me to re-use a lot of components and combine things in different ways. My Photoshop file for the Leviathan mockups was over 70 layers. (Though a typical mockup only uses about 1/3 to 1/2 that many.) Then i switched back to using Illustrator, because the Photoshop file was getting too big to manage.
Key concepts you'll need to learn are layer masking and the different layer blending modes. Layer masks allow you to "mask off" a shape or texture using another shape. It's a very useful technique and it's how i applied all the figured wood textures and graphics to the Leviathan
body shape. Blending modes allow you to control how the colours and content of one layer blend with the layer(s) below it. This is how i do tints and bursts, and simulate the stains on figured woods.
All of the bursts i did are done using layer styles (inner shadow and inner glow).
There's a lot more that goes into it, but it's hard for me to condense 4 years of design school and 12+ years of professional experience into a brief tutorial. A lot of it has to do with knowing how colours and textures will interact, and choosing elements that are complementary.
