To make it from scratch, export uv layout from blender to a file. Then you have guidelines to follow. White is no shadows. Paint grayscale to add "shadows" to the areas that should have shadow. Use feathering/gradients/airbrush to make it soft, no sharp edges.
Naturally the professional bake the AO within the software, so the software will find where the shadows should be for you. You can do that in Blender. it is a little confusing and hard to do, though. Then of course, for more detail you paint it on. Here's a page on baking AO:
https://blender.stackexchange.com/questions/13956/how-do-you-bake-ambient-occlusion-for-a-model
(but of course professionals use software like Substance Painter instead!

)
You can also do it in texture painting in Blender too, to paint it on place on the model itself. Then you would choose AO as the texture layer so you see the b&w on the object instead for your BC. It may be easier to do this than in Photoshop as you can see that the things go where it should be.