The story that's always told of the Western Front is about the trenches and the kind of warfare that arose. But what I have heard so little about is what the predominant tactics were of the armies before they started digging trenches. I know that casualties were very high due to the conventional use of cavalry and large units against the new technology of the machine gun, but that sentence is pretty much all I know about the combat before the trenches.
I answered almost the same question [here] (https://www.reddit.com/r/AskHistorians/comments/4rm3st/in_the_battle_of_the_frontiers_and_the_first/).
I know that casualties were very high due to the conventional use of cavalry and large units against the new technology of the machine gun
The performance of cavalry was certainly mixed in the opening days of the war, but this had more to do with misuse by higher command, communications difficulties, and poor doctrine than from "charging machine guns" as stereotype suggests. As for Large Units, this was due more to the range of new weapons (units could be engaged on the march) or poor training (particularly the French) than from a deliberate decision to use tactics from the 18th century in the 20th century.