Although your Empire usually begins the game with plentiful cash on hand, this is often expended in a few turns. Eventually you need to place your finances on permanently sound footing by making a profit. Selling materials is always more profitable than selling resources. Anything produced by industry is considered a material.
The best material to offer for sale depends on your Empire’s current needs and may change turn by turn especially at the beginning of the game. Although, like all materials, fabric is needed for expansion and development, it is often the best choice for selling early in the game. Most Great Powers are able to make fabric at an early date, and it is not as much in demand for development as are lumber and cast iron.
Using your computer advisor to make the choice is sometimes a good idea. However, your advisor does not know the details of your planning. For instance if you are saving fabric to recruit labor in a few turns, your advisor just sees a large stockpile of fabric available for selling.
As your Empire develops, your industries will begin producing extra materials. Then you can offer a variety of materials for sale every turn.