One of the most important things when it comes to any form of art or 3D art is reference and materials to work from.
One project I am working on requires buildings and architecture, so I made sure I got hundreds of reference photos.
Some of the photos/references taken
With these reference photos, I can extract information about objects, their texture, their relative size and use this information to create new assets.
Using a programme such as DDo, Substance Designer or Crazy bump, the texture from the photos can be lifted and specular, bump, diffuse, normal and ambient occlusion can be made. If the texture requires repeating for memory conservation, I use Krita's tiled texture tool to make textures seamless. These will be important for creating and covering large areas of a model like a brick wall to give the illusion of there being much more than just the single texture.