All with all things there are variations. The technology level you are describing sounds akin to that of WW1. This is where trench warfare really started, for the first time the major powers were faced with an enemy with a sufficient level of technology to decimate an open charge. As a result trenches were dug to provide cover from fire.
The trenches of in early 20th century warfare ranged from about 30 metres to several hundred metres apart. This would depend very much on the geography and geology in question (and how it could be turned to a tactical advantage).
However, the front line trenches were not the whole story, in addition there was a massive infrastructure of supply trenches to allow troops and supplies to be moved back and forth in safety from the reserve lines to the the front.
Finally trenches were often underground, as the lines became more permanent soldiers looked for more ways to defend and attack. Tunnels were dug both under their own lines to provide additional cover but also towards the enemy trenches. There are some devastating examples of what happened when one side managed to undermine the other!