Here area couple of node groups I often use.
The AO node gives some nice contact shadows and works great for adding a little shadow detail to character models. Simply put the AO node between your base color and the principled BSDF to get the effect.
The blur node can blur an image texture. It can for example be used for blurring an HDRI where you don't want a detailed HDRI to be reflected in eyes or other objects.