A few stream of consciousness tips for Photoshop compositing:
—Start with your render from DAZ Studio, which I do at mostly 9000 X 6000 DPI, saving as PNG (this will be at 72 DPI and consequently huge in dimensions, but that's okay as you'll reduce it later).
—PNG preserves transparencies (alpha channels), essential for compositing backgrounds, secondary images, etc., and is a lossless file format—never, EVER save as jpeg.
—Open image PNG in Photoshop, duplicate layer into new document, save as PSD at 72 DPI.
—Do all editing with multiple layers, never altering original layer; layers are your best friends.
—Layer masks are your second-best friends; use the paint brush for opacity (white), transparency
(black) and shades of gray (semi-transparent) instead of the destructive usage of the eraser.
These are the basics for DAZ layers in Photoshop. I'll have more tips soon.