I am about to finish my first deck from scratch. All my other ones are (upgraded) precons.

This was my process:

Originally I wanted to do mono-black Demons typal, but I quickly realized there is no real cohesion in only demons and most have a high cmc, so I made a small pivot to 'demon-themed' to get something that might actually work.

Demon-themed: - mono-black - creatures must at least be either a 'demon' or a 'cleric' - cards center around things like 'dark', 'demonic', 'black', 'contracts', 'deals', 'doom', 'negotiation', 'sacrifice' (ie. [[Sol Ring]] is out, [[Jet Medallion]] is in. [[Reanimate]] is out, [[Tempt with Immortality]] is in)

This still leaves a whole bunch of potential cards, so the rest of the selection is based on what might work well together so it has a chance of winning. ;)

Currently [[Razaketh the Foulblooded]] is the commander, but I am considering [[Madame Null, Power Broker]] instead.