Step 1. Realize there are no souls. But once you’ve done this, you must question the role of the mythical soul. If your soul is your essence, your immaterial self, lets chock it up to your mind and or ego.
Step 2. Why would you want to sell your mind and or ego? If there is anything that separates you from the rotting bag of flesh next to you, it’s your individual potential, stored within your mind and or ego. Rather than sell it, develop it! Find something you are interested in and practice that. If you can, find a way to monetize it.
Step 3. Find success. Success differs from Satanist to Satanist. Identify what it means to you, and pursue it. When you have achieved it, make a new goal. Your ultimate success is your own happiness, authority with as fully developed & healthy sense of mind and or ego as you can achieve within your own genetic restraints.
In the end, the act of selling your soul is to achieve some measure of success, you can symbolically sell it in the ritual chamber, or make a pact with yourself. Either way, YOU are the single most important key. Turn it already!
Hail Satan!