What does the layout of a trench look like from World War 1?

Well, it would probaly look zigzaggy as not all the trenches were built straight, this was to prevent major damage from the enemey soldiers.

Try to imagine a tree with spread out branches.

improvement:

Here is an example http://www.spartacus.schoolnet.co.uk/FWWtrenchsystem.htm

also their were michine guns around the trench