Photoshop tutorial: Back-to-basics photo illustration techniques

Step 14 Create more depth and volume by adjusting the opacity of the background layers to between 80-40% on the upper right section of the Layers Panel. This will fade the background layers a little, giving the entire visual composition a 3D-like quality. 

Step 15 Masking is another method that you can use to enhance the relief and 3D qualities of your work. You can adjust opacity on certain areas by masking your layers. To apply a layer mask, click the Add Layer Mask tab on the bottom of the Layers Panel. Use The Brush tool (B) with a Black colour swatch to mask layers. Adjust the brush softness, size and opacity according to your preference.

Step 16 Finish up with more details, textures and visual elements using the same layering and styling techniques. Attention to detail is very important if you want to make your work stand out. It might be time-consuming but your patience will definitely pay off once you see the fruit of your artistic labour.