If you die and then get to 5 minutes on the timer that goes up when you kill enemies, whatever amount of XP ("tech scrap") you had when you died is multiplied by 1.5.
If you get to 7.5 minutes, it's doubled instead. The cap is 9.99 million (so always get under 10 by spending/banking XP, before doubling again).
Since repeatedly doubling your XP is exponential growth (doubling ten times = 1024 times more XP), how much you start with doesn't even matter much. Normal farming only matters to the point of getting strong enough to comfortably do the XP duplication without accidentally dying (since your XP will be on the floor, accidental deaths will be very bad).

Pretty quickly into the first area of the game, you open up a loop back to the first medbay, a door behind two flying blue robots. These two are going to be the enemies you die to on purpose over and over again.
Doing the loop through the first factory (not going downstairs) and killing all enemies along the way is the fastest way to increase your timer. The timer doesn't tick down while you're in the medbay.

Before you have a high weapon skill and an upgraded weapon, you're likely to need 3 full rounds to get to 7.5 minutes, later on you'll only need 2 and can even skip a few more out of the way enemies. Cut the right arms of Astronaut enemies in the first stage (added by free DLC) a few times to quickly upgrade your weapon to level 2.
Sprint/jump attacks are extremely useful for doing this fast. Once you have high enough damage, it gets faster to no longer cut enemy limbs, and no longer even bother scrolling for enemy weak spots.
Grinding to level 150 or so should be more than enough for the first playthrough. You can return to this factory loop later (unequip most health upgrades to die faster to the blue robots) and grind all the way to around level 600 which is about the maximum you can ever use even in NG+++ (the highest NG+ cycle that still unlocks more implant slots).

If you want to do NG+ cycles, I highly recommend using twin-rigged weapons as soon as you get the first one. Cutting the final bosses right arm gives a very overpowered twin-rigged weapon, so that's the best skill to level.

The Good, The Bad and The Augmented DLC adds a lot of very high end, high core power cost implants to make more use out of being ridiculously overleveled. You can also get an amazing twin-rigged weapon very early by just doing any stage with the "arms race" modifier. Break crates in Episode 6 of the DLC for a farmable source of "Kinasthetic Amplifier V5" which increases your damage AND the rate you gain weapon skill at. Since you don't care about normal XP gain methods AT ALL, weapon skill gain rate will be the main thing you want.

Have fun not caring about XP as you play most of the game! No warranty provided, actually caring about XP is usually a source of enjoyment in RPGs ;)