How did the infantry operate on the battlefield in the beginning of the war? Was a squad the smallest unit fighting on the battlefield or did soldiers operate in larger units like in previous century? How the communications between frontline units and higher officers looked like? Were machineguns so deadly weapons in the first months of the war? These are the aspects which I find interesting because there are not many depictions of those first battles in culture.
More can always be said on the matter, so anyone who's studied the period can and should feel free to toss their answers in! For the meantime, the FAQ does devote a section to the beginning of WWI (1914, in case your browser doesn't automatically take you there), and I commend to your attention this specific post from the now-deleted u/elos_.
The matter of communication could also use a more thorough examination; for the meantime, here's a post by u/DuxBelisarius that looks at radio, and also links back to a more general overview of communications during the war.