The Basics Edit
Controlling the battlefield is the act of preventing ones opponent(s) from using a certain unit type. This allows one to operate certain units without fear of retaliation. This is most effective with naval or air forces. To control the battlefield one must have excellent intelligence.
The Early Steps Edit
In order to get the edge you must prioritize targets from the get go. Use T1 bombers and interceptors to limit enemy forces in the beginning and bomb any production buildings you don't want them to have. This is key because if they can build what they want they can counter you. If you can deny certain units you already have an edge in the later stages of the fight. He who can control what his opponent uses has already won the fight.
Keeping it Up Edit
In the later stages use Tactical missiles, artillery, and T3 strategic bombers to continue to prevent your opponent from building certain units. It becomes harder as time goes by, but if you can keep it up long enough you will guarantee victory.
The Impact Edit
Limiting enemy air units makes it much easier to control the skies.It gives you an edge in the information war, allows you to ferry troops more effectively, and protects your base from a logistical strike. This is probably the easiest and most benficial unit type to limit. This allows your vulnerable aircraft to operate without support. For more detailed information read the Air Superiority Article
Naval control is the second biggest one to limit. It is also probably the easiest to limit as well. Controlling the seas allows one to do Amphibious assaults without worry, and allows you to do coastal bombardments. This also makes it easier to limit enemy Experimentals like the Monkeylord. The UEF and Cybran have a big advantage with this as their Sub hunters and Torpedo boats are extremely effective at doing this. For more detailed information read the Naval Superiority article.
Land is the hardest unit type to limit. Mainly because they are the easiest and fastest to build. If one can greatly reduce the enemy land production however, they can win in little more than 20-30 minutes. Because without ground forces one has nothing. If they manage to get large amounts of land units then you can use lots of gunships to quickly eliminate them and take out the factories they were built from. Usually you only want to try to limit land if you already have control of the other two unit types, as it requires nearly as many resources to limit land as it does to limit both of the others. When playing against AI, I believe you can make a maze of walls and that will make it hard for them to get through because of their pathfinding. They could destroy it by walking over it with experimentals, though.
Limiting experimentals is the easiest of the four. Simply destroying economic buildings and engineers can greatly limit enemy experimentals. Sometimes waiting until a certain unit is built then hitting it with a full scale air assault (if you've limited air this is much easier) can cause it to damage their own base as it dies.
Getting out of the Influence Edit
If someone is limiting you the easiest way to get out of it is to use certain buildings or units. If they have limited your naval build a Tempest, Megalith, or Atlantis. This will allow you to quickly reestablish your navy. Likewise Soul Rippers and CZARs help reestablish Air power. The Atlantis can also be used to regain air power, especially if you control the seas. If they control ground, the Fatboys and Megaliths will quickly turn the tables.