Fights can be hard, but not unbeatable.
Since theres no exp, it all comes down to if you can win efficiently enough to gain more than you consume.
Unecessary battles is a waste of time.
Some things I've noticed:
Weight affects how quickly your turn comes up (not really explained as far as i could tell).
If you use less than 50 AP (40-45 for example) you only have to wait half a turn (50 instead of 100).
Most enemies only move on one axis when they move and many have limited melee range, this can be abused.
While enemies can move past one another, they cannot fire through eachother. If used carefully, you can use enemies as shields.
With this i made the following strategy:
Unequip secondary weapon, massive speed boost (but some issues vs some specific high defense enemies).
Each turn i normally do a combination of moving 1-2 squares and/or 1-2 single shots or a burst, then rest to regain 15 energy.
This will allow me to rest twice as often while slowly moving around and shooting (or whatever else i need).
I can often act 3-4 times between an enemy preparing a super attack and the attack going off.
I can allways go full 100 AP at the expense of skipping the next half-turn if needed.
Meditate heals 200 and takes 20 AP, so fits well with this strategy.
Heat wave attack (muzzle attachment) works well on vs bullet resistant enemies and cost only 10 AP but 50 energy. With the double rest, this is managable and i can allways move around or meditate when i need more energy.
If you find yourself close to the enemy:
Strip armor works well vs bullet resistant enemies and cost 35 AP, can be combo'ed with heatwave which do more damage at shorter range.
Hand to hand cost 25 AP and gives you a little energy, can be used situationally (one H2H + 20AP action is still under 50AP).
Moving so that your so that you're positioned 2 squares away from the enemy in both axis will mean most melee enemies cant hit you on their next turn (as long as your not nude).
Turret is a useful companion with good range, but expensive to replace if destroyed. Use it situationally.
Enemies will try to attack the mine as a foe and can be used as a distraction/meatshield, but is also expensive to replace.
Use grenades and vibroblades against bosses as you see fit. You have them, might as well use them.