I rely on word of mouth and random visitors for sales. With very little time, interest or expertise (in marketing) my approach is quite basic - offer domains that I would buy for my own projects and be humane with pricing. The extent of my customer strategy can be summed up in: if a customer has a good experience they will tell a friend. If they have a bad experience they will tell 10. I'm not trying to build an empire with Brandfountain, small is perfect for me as I am very busy with another project.
Not 100% science but typically: length of name and number of words are biggest factors. Category can matter as well - eg 'crypto' names are very hot at the moment.