Creating background color/texture. This process is always the same for me, but I’ll detail it here.
For the texture itself, I use a texture brush which I downloaded online for free. (Can’t remember where—sorry—but Google it and a bunch will show up!) I use the Multiply blending mode in the same color as the background fill to create dimension without adding too much chaos in terms of color pallete.
For the shadow, I use a large round brush with 0% hardness so there are no hard edges. I brush just around the border of the frame, set layer blending mode to Multiply, and reduce opacity (generally to about 50%).
For the highlight in the center, I use the same round brush with 0% hardness, but bump up the size about 100 pixels or so. I generally try to keep it 1/3 of my total canvas size. (So a 1500 pixel canvas would mean a 500 pixel highlight in the center.) Then I set the layer blending mode to Screen and reduce opacity to around 50%.