Bionic Dues

Start the game on Expert,
pick Genji as your pilot (to get epic exo & more firepower),
pick 4 seige exo.
Just missle thru the first level.

Some bots are way better (scientist) than others (cough.. ninja)

First don't do this while doing any iron man achievement (why give yourself an aneurysm)

Second, Make great use of the saves. Never overwrite the auto save when you start a level. Use it to put you back on the main map before the fight.
Third, never get hit, never put yourself in a position to get hit. and if you are put in one (like opening a door), save before hand.

Starting pilot - Rey.
You need to maximize Rey's revive for the refill of ammunition.

Turn 1,
Check your items. Do you have an extra dmg or range items? If not, restart.

You should attack either
Blockade (low enemy count)
Overdrive (your low dmg weapons will probably kill everything in one hit).

(This goes for any other map at the beginning). See a hard enemy (doombots, hunter, sniper bots), reload.
See lots of batbots & dumb bots is usually a sign of an easier level.

Before you finish the level, Save!
Check your reward. Will it help you kill stuff better? Yes? keep it. No, reload and get a new reward.

After 2-3 levels, you should have enough cash to buy a cheap upgrade. If you can snag something that gives hacking, pick it up.
Being able to open locked doors at the start to get equipment is a big plus. (you can drop this mid game).
Again, before opening the door, Save. Does it have a chest, no? Reload.
You should aim for a green item (or blue if you are lucky). Reload your save till you get there. (same goes for the small enemy dropped chests)

A cheap Virus+ is great too (but not necessary). Taking over a Bodybot or Tigerbot can be really helpful in conserving ammo.

if your bot has a pistol (scientist/brawler), make great use of it. Kill movement of the enemy bot, then just use your light machine gun to finish it off.
if your bot doesn't have a pistol, try to use range or corners to the best of your ability.

For most levels, you do not have to kill everything.
Open a door and it's nothing but robots and no exits/chests. Reload and ignore the door.
Exit is in sight and you have enough stealth to bypass everyone, do it.

Ok, now you've done a few level 4-5, you are getting decent equipment.
Start keeping/buying anything that has Trap+ (or Propulsion %+) and try to get some mines. (Use those empty/useless shield slots! but not at the expense of weapons)
1- You will be able to go over mines (and not wasting as much ammo destroying them to get thru)
2 - Once you have about 7+ traps, your mines will start doing decent dmg (300-400dmg).

Don't bother with anything shields unless it has trap+ or dmg%+

This is the order of levels you aim for.
(I once saw a great steam discussion post on the subject but i can't find the link anymore).

1 - Robot Command Center - those orange rewards are sweet.
2 - Bahamut - Hopefully, it's for your mec... (I did my whole sniper run without upgrading and it sucked)
3 - Factory -
4 - Hostage rescue - you can probably get 3-4 items for finishing the level instead of the typical 1.
5 - Whatever helps you more.

End game
Keep bring up your Trap skill. You should get getting 80+ of your kills from it. Feel free to take off dmg/range off crappy weapons for more Trap+.

Try to do 1-2 lion's den if you can. (it's really not that fun doing the last level with 250 enemies to kill)
You can try an Assassination map if you want but due to the small open level, it's really annoying and not worth it. It's easier to just kill them in the final level with mines due to the tight corridors.
Your trap skill should be good enough to kill most bosses with 1 or 2 mines.

On the last level, if you run out of ammo (and Rey revives) then just die. You can go back to it and just kill the remaining enemies (assuming you didn't lose any other maps before).