In every strategy game you need to know what your opponent is doing so you can counter it. Generally you find out by scouting with a bear or the army's equivalent. However there are some things that you can't find out by scouting fast enough, like what army your opponent is at the start of the game. Factors like that will affect your build order and how you play so it's imperative that you find out as soon as possible.
Finding Out Your Opponent’s Army
The first and easiest trick is just hitting the ‘Esc’ button. Whether or not it was intentional you can see the image corresponding to your opponent’s army after the game has begun. From there, you can then model your build order based on that information.
Tech Structures
The fog of war that covers the map doesn't quite do it's job. It is possible for you to ascertain which tech structures have been captured by your opponent and which are neutral. All you need for this trick is a unit with an attack function.
Neutral structures are visible under the fog of war and you can give orders to attack or capture them. If you can see a structure then the game has to assign it a team so that the relevant cursor can come up, Attack or Move in the case of attack units. So if a previously neutral structure now belongs to your opponent you will be able to target it as such under the fog.
These are the two icons for move (left) and attack (right).
The mini-map in the top right corner can be used to issue move and attack orders and is the only way to do this trick. Just grab any unit that can attack and move the cursor over Oil Derricks and if the attack cursor flashes up, you know your opponent has it. You can then assume that they went for a build involving a barracks and given the timing of the capture and their army you can probably guess their entire build order.
Garrisonable Structures
Similar to the above you can determine whether or not a building is occupied by your opponent. This can be crucial when moving your army towards their base.
For example on the map Industrial Strength, there are multiple points of garrison either side of the center giving you two routes to choose from with land based attack. These could reveal your army to your opponent, and do some damage to them along the way. On occasion your opponent will have only garrisoned one side as he went for one Oil Derrick. So you can then take your army along a route that avoids that and attack with the element of surprise!
