Was there a 'standard' trench construction, or a guidebook on how to construct trenches? Is there a noticeable difference between the trenches of Verdun and the trenches of Gallipoli?
^ These answers I've given should be pertinent, specifically the last one.
Trenches varied based on the make up of the soil, the nature of the terrain, and the views of the forces creating them on what their role would be. On the Western Front, Franco-British trenches paled in comparison to German trenches, but that was because trenches were permanent defensive positions for the Germans, temporary 'jumping off points' for the French and British, who anyways had rotation systems to ensure that their soldiers did not spend long periods of time in them. Most armies had guidelines on how to dig proper trenches and field positions before the war, but they underwent considerable change under the circumstances of war.
Is there a noticeable difference between the trenches of Verdun and the trenches of Gallipoli?
At Gallipoli trenches were often hewn out of rock, more Sangars (defensive position made up by rock walls) than trenches, and were built often on elevated ground. They became quite unsanitary, due to the heat, disease and presence of dead bodies. At Verdun, specifically during the battles in 1916, trenches essentially ceased to exist, artillery reducing the infantry to holding shell hole lines, with the hilly, forested terrain creating a somewhat 'decentralized' battlefield.