There are plenty of sources visualizing combat on the western front, but when it comes to the eastern front, they mostly just tell me what strategys were used, not what the combat looked like.
I know that things were "more mobile" but too what extent? What were average distances of engagement? How were fortifications stormed and defended? What was combat like outside of fortifications?
The lines were generally further apart, as the terrain is largely flatter and space is less of an issue (as opposed to key French towns being just behind the German front line in the West). German soldiers commented that Russian fortifications and trenches were less well-made. Artillery was more sparse but more important as soldiers were more likely to be vulnerable for a long period if they were not in trenches.
In the war, all the sides developed their artillery tactics to a great level of sophistication, and much of Germany's work was done in the east as her army sought to use an economy of force, and as it was not feasible to seek a 'decisive breakthrough' on a front so large, using the infantry-based tactics of the West.
Having said that, the line did solidify around key points and set-piece battles, often looking a lot like those in France, occurred. Localities like Gorlice, Riga and Lake Narotch saw such fighting. Usually the Russians had the worst of it in large part because they struggled to develop their artillery tactics quickly enough- they were hampered by a lack of resources, inefficient use of those resources (especially hoarding ammunition), a lack of education for the technical methodologies, lack of aircraft and maps, and snobbery among the artillerymen toward their infantry counterparts. They could often give the Austrians a hard time but inevitably this attracted German support.
The failure to use artillery with precision left then infantry to be mown down by machine guns, and this often happened. Even successful offensives like Brusilov's in 1916 would falter after the troops had moved beyond the areas covered by the initial plans.