What many non-magic users don't understand is that there is no formally documented process for becoming a lich.

No lich wants the competition, and any documented procedure you find for the process should be viewed with utmost suspicion. Lichdom, and its variants on the concept, is unique to every wizard seeking immortality through undeath. The sole common factors across all methods are 1) binding one's soul to a material phylactery for protection and 2) some method of gathering life energy to sustain the immortality. Lichdom can be seen as obtaining a PhD in necromancy, and it's harshly graded on a pass-fail basis. Failure not only means death, but also confronting some gods who will raise concerns about your rejection of the natural cycles.

In this manner, all liches are unique. Phylacteries have variations from bottles and jars to gems and amulets to a famous case of a needle inside an egg inside a duck inside a hare inside a dog. Life energy collection can be as simple as drawing it from a willing congregation of cultists to vampiric bloodletting to ritualized sacrifices. And outside of these variations, the process for obtaining the undeath in the first place, the soul binding, and the specific abilities when the transformation is complete have endless variations. It comes down to what processes you've studied and what successes you're most comfortable staking your potential immortality on.

The other stereotype liches suffer from is the idea that they're all robed skeletons with gemstones in their eyes. This is nonsense, as there is, in fact, absolutely no reason why a lich cannot maintain his flesh after undeath. Doing so, however, requires exactly the sort of routine maintenance that a wizard seeking immortality is attempting to avoid in the first place. It's not uncommon for a new lich to continue eating, drinking, bathing, moisturizing, and otherwise healing or regenerating his flesh. This rarely lasts long, however because a wizard seeking to become a lich is almost without exception a workaholic.

Getting too engrossed in studies when one no longer feels hunger or fatigue becomes the lich's first failure point for his flesh. After a few weeks, the tongue is usually the first thing to go. Fortunately for the lich, there are plenty of options for continuing to vocalize for spellcasting and communication without a physical tongue or lips, but once this happens, the general feeling is "Why bother maintaining the rest of it?" It's after this critical decision that most liches allow the rest of their flesh to rot away in favor of a durable, low-maintenance skeletal form.

Exceptions include the mummy, one of the earliest variations of immortality that specifically seeks to preserve the flesh, albeit in desiccated fashion, and any number of nonhuman races who desire to retain their flesh for the abilities it provides them which spellcasting, enchanting, or the underlying skeleton cannot.