From what I understand, WWI was a big transition point for military theory. The kind of modern combined arms warfare you see in WW2 and beyond (the close coordination between artillery, armor, air assets, etc. Think of German blitzkrieg) wasn’t really developed yet. In the late 19th to early 20th century you see the emergence of new technologies like smokeless powder, breech loading rifles, machine guns, better artillery, and more, but many of the commanders of WWI had their military education of the previous age of warfare, where massed infantry and use of horse cavalry carried the day. So while more modern weapons were being developed, the knowledge of how to use them wasn’t caught up. Also perhaps the commanders didn’t comprehend just how devastating machine guns and artillery could be

The French military at the time had a belief called elan vital which meant that the individual fighting spirt of the soldier was more important than the weapon itself. So lots of early battles the French had massive casualties in such frontal charges for little gain because of this belief in fighting spirit. The British had like 60k casualties in a single day at the Battle of the Somme.

There were innovative officers (ex: US general Patton of WWII fame fought in WWI), but there were also really stubborn commanders (the Italian Luigi Cadorna, who fought no less than 12 battles at the Isonzo River)

So yes there was a lot of “going over the top” as you see in movies, but there was a lot of innovation happening as well. Read about the German Sturmtruppen or the Italian Arditi, who were renowned fighters with unique tactics. So an oversimplification is that WWI saw a lot of archaic tactics and beliefs used, but it also helped give birth to modern warfare.

The military history WWI is fascinating. I hope others can add their knowledge to this comment as well, mine is kind of a scattershot of ideas. Indy Neidell has a fantastic channel called The Great War where they covered WWI week by week in real time over four years.