Marksmanship
The fastest way to raise this crucial stat is to throw knives at crows,
gradually increasing the distance. I strongly suggest this for all marksmen. You
also gain DEX in this way.
Explosives
To raise explosives like fire lay and disarm a mine over and over again. If the
merc's EXP is too low to disarm it, use your explosives specialist and continue
as before. And did I mention "save"?
Health
To exercise HEA, travel (on foot) carrying heavy equipment (weight over 100%)
This can be also done in real-time: put a great load on your merc and have
him/her run around. When s/he falls, wait until his/her energy ("breath")
regenerates and... move it soldier!
Agility
AGI is raised by getting interrupts, crawling with stealth on during combat and
dodging bloodcats' blows.
Dexterity
To raise DEX really quick, find some throwing knives and crows (after some time
they appear on rotting bodies) This shouldn't be a problem in towns
Use crows
as targets. Blades are not consumed and new hungry birds always appear, so pick
the knives up and repeat until satisfied with the result. If you throw a knife
at a crow which is taking off, you lose the blade (wow, it's spinning!) DEX goes
up also by punching enemies, animals or vehicles and repairing stuff.
Strength
STR can be raised by punching, opening crates and carrying heavy stuff (same way
as HEA)
Leadership
Training militia increases this stat notably, especially when you put a skilled
trainer with a less experienced one in the same sector (see: SECTION 5)
Wisdom
This stat is the one most difficult to raise. During normal gameplay it hardly
ever changes. Still, wisdom can be trained by attaching a detonator to
explosives, setting it and then disarming. Of course, there is a great chance
you will detonate yourself in the process. Therefore this task should not be
attempted by mercs with low EXP, and even with high EXP it's best to save
frequently. Fortunately, EXP can be easily increased.