The earliest we have knowledge of as regarding definite details of organisation and tactics used is the Battle of Qadesh, conventionally dated to 1274BC. This is the earliest battle about which we know the commanders, location, numbers, composition, course and outcome. An Egyptian force invaded the Hittite kingdom. Very briefly (as I am on mobile) one of the four columns of Egyptian infantry (overall commander Rameses II) was ambushed on its way to an advance camp by a flanking force of Hittite heavy chariots commanded by Muwatallish II. The heavy chariots rode through the Egyptian column (threatening the life of Rameses II at one stage) and proceeded on to loot the camp. The first Hittite force was exhausted and bogged down as Egyptian resistance stiffened and Ramses brought his own chariots to bear. The Hittite king committed 500 more chariots for very little gain. Finally the Hittites were forced to retreat, where they suffered heavy losses from the lighter, faster Egyptian chariots. Both sides formed up for battle on the second day but the event was indecisive. This led to a peace treaty between the two superpowers of the day.

Source: Qadesh 1300BC, by Healy.

German archaeologists are slowly unpicking evidence of a dramatic bronze-age battle that took place in southern Germany in 1250 BCE (i.e. over 3,000 years ago). It seems to be related to major population movements that took place at the time. Certainly, the genetic and other evidence suggest the fighters came from diverse places across Europe, and were perhaps professionals (certainly not just a bunch of farmers. There's direct evidence of at least 130 dead, but it seems likely that the true number is much greater (as only 10% of the area has been excavated. It seems to have been a bit of a running battle, with a focal narrow point which was the site of the excavation.

http://www.sciencemag.org/news/2016/03/slaughter-bridge-uncovering-colossal-bronze-age-battle