All my low poly art is created in 3D software. I first create all required 3D models for the scene individually, this can include the main subject matter as well as other elements and the background - then add lighting to the scene.
At this point I'm ready to start adding materials, colour and textures if necessary. There will be lots of back and forth - tweaking the models and the lightning to get the composition just right.
Now I'm ready to start rendering the image, this can take a couple of minutes to a few hours depending on the complexity of the scene and will often require multiple renders until I'm happy with the final render.
It will then be taken into a software like Photoshop for final touch ups and color correcting.