Unlike most hardcore modelers, I don't do a lot of 'weathering'. I build the kits 'out of the box' as best as I can, paint them , and then give my armor a 'flat' finish and my planes a gloss [usually] for that 'slick' look. I do some dry brushing of light-blue [testors] here and there for highlights [don't ask why, but light blue provides some interesting effects - just a touch on bolt heads, rivets, ends of gunbarrels, tracks] ands also use a #2 pencil for panel lines and edge-wear , anywhere where a 'gris' or 'dirt' or wear on a panel edge. Colored pastel pencils also help - earth tones etcetera. It's easy to grit-up and 'battle damage' a good kit - but not so easy to restore a 'battle worn' kit to like it was when it first rolled out the door. A light spray of any color or thin white glue followed by a judicious application of fire place soot and ash while wet creates some authentic soot and ash effects - cause it's the real stuff - but it's kinda messy so use lots of newspaper. Brush off the loose dust/grit/soot with a stiff brush after it is dry. A hot nail from a bic lighter flame applied to your war-fighter makes excellent bullet holes. I had a house fire some years ago. I picked some of my old kits out of the rubble. You want realistic battle damage? Build the kits and take a blow torch to 'em, gently. Spray 'em with a hose in the yard. Don't set anything on fire just 'toast' 'em. Soldiers, too. Ewwwww. ... white glue, bits of debris , a broken-off whell, broken tread, mix white glue with dirt/soot and brush on. Rubber cement comes in handy too, and it comes off if you don't like it ... spray fixer/adhesives with 'dust' . Bits of small chain dragged over the wet paint . Like making mud pies - you only want a little bit of 'pie'. Hope this gets you thinking ? Ha!