Before you lay down any weathering. Think about how your armor is worn. Does it rub against a belt? Does your weapon rattle against a specific plate? Also, thinking about the "adventures" your Mando has been through can help you think up battle damage. Did you take a blaster bolt to the chest or helmet? Maybe a predator scratched your leg. (A lot of Mandos seem to run into a three clawed beast. To this day, no one knows the creature's identity.) If you're really comfortable working with sintra, you can even add physical damage to your plates. Maybe your belly plate has a stab wound or you took shrapnel to the shoulder. Be careful not to go overboard, especially if you're working with 3mm sintra. Too much damage and they might actually break. The physical stuff will allow paint to pool naturally, making weathering even easier.
Most people won't hear whatever story you've developed for your character so your weathering can tell that story for you.
Some great points above.
In the past, I've made my weathering very physical, as in actually pitting/scratching/scraping armour or helmets before painting. Learned a few tips and tricks with some cheap files and rasps as well as with my Dremel tool.
Weathering can be done as cheaply as getting a bucket, filling it with dirt and small stones, chucking some pieces inside (that aren't resin or too fragile), and rolling it down a hill or wherever. If you're using leather or vinyl, make your pieces and then scrunch them up and sit on them for a day. All of the above for your jumpsuit and other soft parts. Get your boots first and wear them around to break them in. Go kick some stones or shovel some dirt while wearing them. Then go back and touch up all the damaged spots with a lighter shade of dye or paint to help accentuate the marks. There's not really a wrong way to do it, so long as it gets you the result you want. Sandpaper works well on soft and hard bits - great on armour if you've been dragged around. You can mist your stuff with spraypaint to give it a grimy appearance. Layers, layers, layers!
Definitely heed the above advise and think about your story. It'll help you figure out how much or how little to weather your stuff.
