Photoshop carries a dichotomy in that while on the one hand it is an application of extraordinary precision on the other it carries within it great potential for generative visual creation.

Plugins:
Especially staggering are the results that can be obtained with photoshop plugins. Most of these are freeware and can be downloaded from the internet. Some are shareware while others are registerware and can be expensive. Plugins can perform feats from colorization and texturing to image redefinition, such as various tiles and flips and chops. There are plugins that will 3D your work, add lighting and lens effcts. There are also plugins that will create new shapes on an empty layer. there are plugins that will create pencil sketches and outlines from your images.

You should however be aware that

plugins, when misused can cause absolutely horrifying results. This is especially true in the case of colorization plugins. So caution and judiciousness should be your keywords.

Customshape tool and brushes:
The creative usage of both these tools will give you an array of generative shapes and textures. The customshape tool can also be used in conjunction with vector applications. There are plenty of brushes and customshape presets that can be downloaded from the net and then tweaked and redefined to personal needs.

Stock Photography:
I find the mentality of having to create everything from scratch competely outdated. The name of the game now is resource utilisation. Search for images and indeed all sorts of things created by others, be inspired by them and see where they lead you...