Hi Erad, here's a thing I typed up over at Armorama...hope it helps!
All of my rubble as always, tends to look the same, but for me it works.
I have a list of "ingredients" that I use for my rubble:
-Smashed plaster (poured into sheets, and tinted with brick coloured acryllic paint, then put into ziploc bags)
-Brick coloured gravel, purchased at Michaels Craft Store, it's from the xmas Village Collection
-Fine and Coarse Rail ballast
-Bits of broken flat toothpicks (I prepaint several hundred different colours and break them all apart, and bag 'em for later)
-Bits of bigger pieces of square balsa wood (for beams)
-Bricks (either hand made or purchased)
-Any other odds & ends, depending on the situation eg: shingles, etc
Now all I do is just add a little bit of each into a jar, shake it all up, and pour my rubble onto my base, adding stuff like jerry cans, crates, bigger beams, etc. Once I have it the way I like, I mist with water, to wet it, then start adding my white glue/water mix everywhere to glue it down. This usually takes a few applications. While still wet, I'll add the really fine sand ballast for that gravelly rubble look. Once everything has dried, I add a wash of burnt umber/black artist oils, followed by some drybrushing and a topcoat of MIG Pigments Brick Dust.
"There you go with those negative waves again!"