I'm chiming in more for 'pre-modern' era Japan rather than the areas you explicitly stated, though since you said etc. I'm hoping this will work for you.

Though not an extensive explanation, Stephen Turnbull's The Samurai Sourcebook states that Japanese armies were definitely capable of issuing orders throughout the battle, either with drums, shells (used as horns), or flags, and to a lesser extent, gongs and bells. There would be systems set up before battle to explain what certain rhythms/calls/flags meant, as well as sequences and combinations that were understandable only by the same side - it wouldn't do well if your flag read "Flank their left side" in plain text for the enemy to read. Turnbull also goes on to say that messengers on horseback were also used to relay information from the general or daimyo to the individual commanders, or samurai. Understand that, whilst there were individual 'sub'-commanders that commanded a 'unit', a lot of the time the leader would be moving forward an entire line of attack/defense, rather than a small group of soldiers. This proved especially true during the Sengoku period, whereby larger armies composed primarily of peasant ashigaru made it a necessity to communicate to a wide group of footsoldiers.Messages might have been relayed half by writing, half by word, and decoys were possible as well, to prevent the leaking of information if the messenger was captured and tortured.

Similarly, during battle, a command hierarchy existed, as did regulations and general rules, and as was expected, authority was followed. If it were a daimyo who called for the army to assemble, they would be the commander, if it were a loyal retainer, they would command, and so on. The commander-in-charge would, before hand, also set up a plan, possibly outlining certain features (e.g. forests, mountain slopes) - an example of this would be the fourth battle of Kawanakajima, between the two daimyo Uesugi Kenshin and Takeda Shingen - one of Takeda's generals formulated the plan of driving Uesugi's army down from a hill on to a plain, where Takeda's army would be waiting in ambush.

It really depends on the army, of course. The Roman army, even in antiquity, was renowned for its flexibility and its ability to adapt to emerging situations. The second century Greek author Polybios even cited this as a key factor in the extraordinary success of Roman arms. Probably the most famous example of this is the Battle of Cynocephelae in 197 BCE against the Macedonian kingdom. The battle essentially turned into two battles, with the Roman left flank slowly being pushed back by the Macedonian right, but the Roman right gaining significant success over the Macedonian left. The end result is that the Roman right ended up behind the Macedonian right, and a tribune on the right noticed this situation, peeled off the soldiers under his command, and charged into the back of the Macedonian right, scattering them.

Check the image I linked to see a good visualization. The fact that the tribune had the initiative and capability to react to emerging battlefield situations was key to the Roman success in the battle, and demonstrated a clear advantage over the more rigid Macedonian command structure. And this situation is hardly unique, as if you read Julius Caesar's Gallic Wars you see that he was a master of reaction and frequently his victories came by changing the plan halfway through the battle.

Not every ancient army was this flexible. The Battle of Cunaxa was in a civil war between the Persian king and a pretender to the throne, who had a large body of Greek mercenaries. The Greek mercenaries won handily in their sector of the battlefield, but after driving their enemies off the field more or less just sat on their spears, and weren't aware that the rest of the pretender's army had crumbled until told to surrender by a member of the king's forces.

I would direct you to this thread which I commented on yesterday [about how much command and control generals had] (http://redd.it/3d9hjt). It is a similar topic to your question, and there is an answer there dealing particularly with the Romans.