What effects did the trade policies of East Asian countries have on their development?
This is a very general question on a big topic. Do you mean historically, in the post-World War era, or today?
Historically, East Asian countries had rural economies based on food production, especially rice, with cash crops being primarily opium. In the Indochina area, many wars among the Thais, Vietnamese, Lao and Khmer were as much about the control of the opium trade as for territorial expansion.
In the early modern era, East Asian countries were largely colonized by the French, Dutch and British. Trade policies were set by the colonial powers, and tended to concentrate on tea, spices rubber and cloth goods. This brought more money into the local economies, but of course the economic gains were mostly to the benefit of the colonists and the trading companies in Europe which handled the goods, shipping, etc.
In the postwar era, Southeast Asia was riven by anti-colonial wars, with European countries and the local anti-colonial forces struggling primarily over control of rice and opium production. In Indochina, if the French could control the rice farmers and the opium business, they could keep control of the population. If the anti-colonial forces gained control of those crops, they could use the loyalty of the farmers for manpower and the money from the opium trade to finance their revolutions. Rubber production was also a major cash srop in the region, and total control of that by colonial powers was a sore point. Other East Asian countries had similar problems, while some others had an easier transition into the modern world, such as Singapore. The effects of changing trade policies and the loss of colonial control by war and changing economic conditions in Europe brought more money into the indigenous population, and economic self-control meant eventual political self-control.
Modern trade policies vary a great deal from country to country . There are some links below which might help. Sorry if this seems a vague answer, but it's a pretty vague question.