As Peter Jensen would say, you have to learn to sell to the masses. I do best selling things personally when an item has mass appeal, not just to the category it is in and when it is an item that almost anyone would like. Then you use limited resources to put it out to a few hundred people and with enough people it will start to sell. Then if it works like that and you want to start putting more into marketing, you set yourself up for something that will probably work.