I've had a little experience.
I use sand paper to rough up some areas, scissors, to take out little bites of fabric. Use a small flame such as a candle or wood matches the singe the fuzz after that.
I don't have an airbrush either, but I've a couple cans of hobby spray paint. Dust the straps with a can of that. I mask spots by tearing small holes in newspaper, place over object you want to "age" and dust with a fine mist. It makes very convincing stains.