When I started playing, I'm pretty sure nobody told me I could get a sh*tload of xp by communing with the spirits of some objects that can be found in both friendly and hostile areas (most are potted plants, ferns and mushrooms, but you will also find some statuettes and random ritual objects). Maybe the tutorial didn't pop up. In case it didn't for you either, this guide is for you.

When you encounter some objects you will see that the game prompts you to interact, but no interaction will happen unless to shift to umbral vision. Do so and then interact. An animation will happen.

And presto! You have some xp points, and as you advance in the game you will see that most of the points that you spend on skills come from this snorting... erm... communing with the spirits.

Hope this is useful, and may Gaia be with you!