One of the major problem in DF is the lack of any necessity or incentive to export raw materials from your forts. It is currently far to easy to get your own manufacturing and crafting lines up and running and for you to process all of your raw materials into finished goods. The growth of a proper settlement should begin with one or two raw material industries such a lumber or food which transition to intermediate products like metal bars and culminates in the finished goods exporting apex. At the same time imports to a settlement should start with finished good and transition to raw materials to support the domestic industry. A few of the factors that need to change to help bring this about.
Immigrants for industries that don't exist - the current random immigrant wave includes skills for a great deal of specialized crafting which the player hasn't actually started doing yet which both entices and facilitates creating a diversified economy. Their is some counter logic of course, craftsman want to move to an area ware they would have a monopoly on that skill and could gain reputation out from under the shadow of their superiors. But the current migration pattern feels far too random and unrelated to the natural resources or activities of a fort.
Almost no overhead to most industry - almost all workshops take nothing more then a block to make so physical overhead is practicably nil, the hollowing out of storage space and creation of bins is more of a limiting factor then the workshop itself. More tools or parts for making workshops would help along with more time needed to construct them, for one I think many workshops like the craftshop should be made with one or more tables as they are visually implied to have tables.
Profitable production with neophytes - almost every industry will turn a profit of 100% with an unskilled peasant as even without quality modifiers the finished 'form' of an item is worth twice that of the raw form. Better workers just make more profit. Three solutions present themselves, make the dabblers fail in occasion and lose a unit of raw materials, have bellow normal quality levels which have modifiers smaller then one, or limit the highest profitability crafts within a profession to higher skilled members of said proffetion, example Helms currently have a value modifier of 15 and greaves 30, the helm could be made by a crafter of Competent or higher level while greaves would require Talented or higher.
Traders crave crafted goods - trade wagons negotiations with your home civilization always offer large bonuses for one or more craft goods, they almost never offer premiums for raw materials which presumably the larger more developed cities should want. These premiums should start with exclusively raw material bonuses and transition to crafting goods as your fort grows in population and wealth.
Lack of Market saturation for sold goods - The bidding systems in which you push up the bar for items you want more of and in return pay a premium for is a good if primitive means of showing supply and demand relationships but no equivalent occurs (to my knowledge) on the selling side of the equation. This could work by having the sales you make one year (actual quantity of goods sold) affect the premiums offered the next year. That said the premium offers need to be far more consistent from year to year, a minimal simulation of what the economy of the other civs makes and needs should occur so they have consistent purchasing patters. Then on top of that pre-existing demand the sales you've made can depress prices. This dose two things it can make reliable focused industry viable, if you know food is going to bring a premium over not just one but many seasons then creating a food export industry is attractive. Its also self balancing to a degree as your exports can't grow in an unlimited way without depressing prices so long term diversification is also encouraged producing the desired transition to crafting.
Overly expensive imports in early game - I would consider importing certain commodities if caravans would only off versions that are in my price range. Platinum decorated spears and giant spider silk bags of flour are simply outside of my price range in the first few years. As I'm only interested in utility for these critical tools the decorations are nothing but dead-weight. Its quite stupid to offer these fancy items to a group of piss-poor settlers, the caravans are wasting valuable space that could be used for useful items. Caravans should bring predominantly finished goods but those items should be simple utilitarian ones at first and gradually increase in quality as your fortress wealth increases. The goal of any logical caravan would be to offer a fort items that are beyond its own capacity to produce, so once your able to make basic weapons the caravans should bring higher grade ones so your presented with a real strategic choice to buy high quality or do without and save money.