Honestly, I plan my trap usage around the fact that Underrail is a sequential, turn-based game. Most commonly, I'll set a mine at a choke point with enough room to move around it, then I'll aggro the enemies while standing right in FRONT of the trap.
Given the current state of AI in the game, melee-centric enemies will then rush to attack me, piling up at the choke-point (and into the blast radius of the mine). Then, the next turn, I'll retreat back past the mine and out of the blast radius. That ensures that when the mine detonates, as many enemies as possible are in the blast radius.
It's not the most ideal strategy, but it was invaluable during my Trapper's progress through the last few areas in Junkyard. Those Mutants were a huge pain to kill conventionally.
An alternative I've had some success with is using traps in conjunction with a high Stealth rating. With a high enough Stealth skill, the player can sneak up on enemies and set a trap very close to them. Almost impossible to do without the Trap Expert Feat, due to the long trap-setting time, but particularly handy for set-piece battles (the Raiders under GMS, for example, or the Toll-Takers in mid-Junkyard).
The easiest method of use, at the moment, is when ambushing Sentry Bots. Due to the very predictable patrol pattern that most Sentry Bots follow, it's easy to set an EMP Mine in an area that they're sure to pass through. Then, once the EMP mine detonates, it's a simple matter to leap out and spray the incapacitated Bot with a large number of bullets.