I wouldn't start hacking into your models, the best place to start with battle damage is to paint on nicks, wear and tear, and the like.
None of this is gonna work on a metallic armour but if you go with any non metallic colour scheme you have a few options.
First pick if you want the wear and tear to look new or old, if new chose a silver, if old a brown. Then depending on the main armour colour of your scheme make it either a light or dark brown/silver. Either by very selectively painting it on, stippling/drybrushing it on, or getting a torn bit of the fine sponges
GW used to put in metal blisters (I'm sure you can find something else appropriate for this).
You want to then paint/sponge on the battle damage where it's mostly going to actually be found. Knee pads, armour trim, the shield, etc. Highlighting the top edges of these 'chips' with a lighter colour or the bottom edge with a darker colour will add a little more of a three dimensional look to it and make it appear as if the armour has chipped. You can also add scratches with a fine brush by simply streaking a line across a flat surface and again highlight/underline it (works great for the shields or a chest plate and really adds character).
A couple of old examples of my stuff using that technique:
And a better one that isn't mine but the top edge is a really good example:
You can also try an actual chipping medium from any of the companies that make them (Vellejo does and you should be able to find that everywhere) which can give REALLY cool results but requires.. well not actually more effort it's a really simple technique but you'll have a lot to learn to get it to work and probably requires an airbrush. Basically the idea is you paint your model silver or rust brown or whatever, cover it in a chipping medium, then paint the actual armour colours over that. Then with a wet, stiff, brush you can scrub off the chipping medium and the armour layer on top of it, leaving the under colour visible.
If you still want them even dirtier weathering pigments are really easy to do and make everything nice and dusty and how I did these bases:
Basically it's just a 'dust' made of the part of paint that gives it colour without any of the liquids that make it paint, you can easily drybrush it on and then dab it with white spirits to lock it in place while keeping the dusty appearance.
If you've wondered about the cool streaking you've seen on the tanks that's another fun weathering technique for rust streaks, oil stains, etc that are probably a fair bit more advanced and not really all that useful on infantry, but you could look at a company called MiG who does a lot of these effects. If you did want to give it a try though the techniques are basically to varnish your model, then use an oil paint to dab a little colour on, then with a brush wet with white spirits you brush the dab of paint in a single direction and take most of it off, leaving only a little tint of colour where it's been streaked down.
(Which is what I was doing on this bad boy who I will jump at any excuse to post
Good introductory paint on chipping with Duncan:
https://www.youtube.com/watch?v=Onspoa5N6Zw
Another simple one with a sponge:
https://www.youtube.com/watch?v=aNBeRdi_cf8
A Vellejo chipping medium tutorial/review:
https://www.youtube.com/watch?v=9CNhG4H38gI
(They mention the hairspray technique, and there is one too with salt, neither of which I mentioned because I myself have never used them but might be worth googling)
A tutorial for pigments:
https://www.youtube.com/watch?v=EU7jeb9drmM
And a quick oil streaking just because:
https://www.youtube.com/watch?v=qwVvHYn5BvE
You'll be able to find a lot more in depth tutorials for all of them on youtube, I just looked for the quick and simple ones.
I also cannot recommend enough The Weathering Magazine, especially since one of it's recent issues is a back to basics theme.
https://www.migjimenez.com/en/english-version/1404-twm-issue-21-english.html
Hope some of that helps, I
ing LOVE weathering and really think we mini wargamers have a lot to learn from the historical folks with their oils, enamels, pigments, etc