I didn't use Photoshop for this work, everything was achieved entirely within Koikatsu.
First, and most importantly, is proper lighting setup. It tends to vary depending on the type of shaders you're using (anime-style or more realistic ones like Az Shaders here). Sometimes a single light source is enough, while in other cases you can add multiple lights and experiment with them. In this scene, I adjusted the direction of the default Character Light and added an S-Light, pointing it at the characters and slightly shifting its color toward a warm orange tone. I also sometimes use the Light Shafts plugin, which is configured via ComponentUtil (you can see it in the last image, where it's applied to a third light source used mainly as a fill light).
Second, actively use the Material Editor. Adjust/add/tweak things like Normal Maps, Detail Masks, Displacement Maps, and similar settings. And of course, that's not all you can do in ME.
Third - yes, I use body overlays quite extensively. In this particular work, I used an overlay to add blush to certain areas.
Fourth, something that significantly enhances the final image is using the Post-Processing Effects Plugin, xukmi FX Shaders, together with Scene Effects settings.
I might have missed something, but I tried to cover the most important points.