In my perspective the Left Hand Path, (without mentioning the Vamachara initiated by religious outcasts in India, which consisted in a large compendium of spiritual practices and mysteries considered transgressive by the rules of standard forms of Hinduism, very roughly speaking) is the path of Separation, in opposition to the path of Dissolution (taken as Union by RHP practitioners). Which basically means going against the grain of the cosmological momentuum, knowing that the cosmos and it's creator(s) aims to engulf, assimilate and dissolve every consciousness that dwells within it's realm. Because the Macrocosmos is the Dream of another mind.
I personally like the Qabalistic reference to approach the mechanisms of both paths. The Dark Path, the Draconian (severity) Path, is the path of knowledge, ownership, to preserve and enhance individuality to heights beyond the Godly. Symbolically it could mean that this is the path that fulfills the Serpent's proposal to mankind with the offering of the Fruit of Knowledge. Going through the left pillar of the Tree of Life will lead the practitioner to the Tree of Death/Knowledge, the Qliphoth.
It means to take ownership of your own alchemical process and explore the dark evidences that exposes the very existence of the Cosmos as a hack full of flaws, backfires and accidents caused by a consciousness that cannot be taken as anything other than downright lost and incompetent. Honestly, to me, it means to radically deny the sugar-coated falsity carried by any conjecture about external reality, including philosophies, doctrines, religions, etc. This attitude will lead you to the Sinister Path eventually. It means to be full of Magic and Spirit, while accepting no hope beyond the Self's actual capabilities whatsoever.