The Choson are a fairly well-balanced civilization that can be effective offensively or defensively. Their greatest attribute is cost efficiency, allowing you to make an enormous number of troops to overwhelm your opponent for relatively little cost. However, this also makes the Choson's greatest challenges circumventing the population limit and avoiding bottlenecks.
The Choson are most popular in Deathmatches, where many new barracks can be built quickly and an army raised rapidly. In standard games, the Choson are still a viable civilization, as they are very versatile. Due to their success usually being tethered to their numbers, they are not an ideal civilization for rushing, though rushing is not impossible.
In terms of resources, the Choson have no inherent resource-collecting bonuses, but they can become proficient at all resource collection by researching everything up to Irrigation, Artisanship, Coinage, and Fortification in the Iron Age. Due to their range of strengths, The Choson require a large number of villagers to quickly gather wood for building barracks, food and gold for Priests and Legion, and stone for Towers.
One-on-one, Choson units are not likely to find much success against most other units in the game. While this makes them significantly less expensive, it also means that the Choson's best chance for success is simply to overwhelm an opponent with an enormous invasion. To accomplish this, many seasoned Choson players simply build an enormous number of barracks, bring their population to the limit minus one (49 in a standard game), and then quickly scroll through every barracks they have and raise a large army (until the existing population reaches the limit, new troops can still be trained, and any whose training began before the limit was reached will still appear). This army, though slow, is almost guaranteed to overwhelm any other civilization in the game. Of course, this also puts the Choson at a disadvantage in any situation where there may be a bottleneck, such as a land/water bridge or through the use of transport vessels, where the Choson's numbers can be negated in a situation akin to the Battle of Thermopylae. Thus, the Choson tend to be most effective on open highland maps.
"Trickle" strategies, where a smaller number of troops are continuously sent in, are not generally effective, as more powerful enemy units will easily defeat the incoming Legionnaires, and while it may keep an enemy occupied temporarily, it will wind up being expensive in the long run and a major drain on resources.
Another strength the Choson possess are their less expensive Priests (85 Gold instead of 125 Gold). Priests can be challenging to use in battle, but pair well with Legion. As Legionnaires overwhelm an opponent, the Priests can stand at a distance and convert enemy units while avoiding direct battle.
Defensively, the Choson's greatest advantage is in their towers, which have a larger field of view than a standard tower. This allows the tower to start attacking incoming enemies sooner, and hopefully stave off, or at least weaken, an incoming attack force.
If a defensive strategy is favored, it is best to rely on towers, though new infantry can be trained and kept on hand in the event of an invasion, but are most effective when their numbers are large enough to overwhelm an opponent.