Wanted to share some of my process.
Did some Google image searching on keywords: Unreal, Victorian, Machinery, Factory, Art Nouveau, Robotics, Mountains, Streams, Abandoned, etc.
Thumbnails: trying to make some sort of mess with shapes I like from my research. Sometimes I'll cut and paste straight from my research into a thumbnail. From there I'll blend the photo image in by painting into it and using a lot of Levels Adjustments in Photoshop.
The images above can be found on my blog: http://iantolmay24.blogspot.ca/
Once I find one of my thumbnails working I cut and paste elements from the working image into a new psd. I then mix around multiple layers of these elements with different blend modes or gradients in photoshop. This in turn creates another mess which lets me see how that one element I liked, can evolve into something new.
Sometimes my thumbnails go nowhere as seen attached.
The paint-over process on the 3D block-ins which have been provided by Epic is tough for me to approach. It's hard for me to get an idea of what to paint; so this where making a mess proves to be fun. I'll copy and paste elements from my thumbnails into the 3D block-in images. From there I make a mess till something starts to come out of the shapes and layers with their respective blends.