A raw denim doesn't ask for much to age well, honestly. The patina happens mostly through wearing and natural friction, not really through complicated cleaning techniques. What helps is just letting the denim breathe and develop without too aggressive intervention.
For maintenance without regular washing, what really works is aeration. After you wear your jeans, hang them in the open air for a few hours rather than throwing them straight in the dirty laundry basket. That eliminates odors and moisture without damaging the fabric. If you really need to clean between washes, a light dry brush with a soft brush is enough to remove dust. Frankly, a lot of people make way too big a deal out of this - your jeans will handle fine going a few months without being washed as long as they dry properly after wearing.
When you finally decide to wash it (yeah, you'll have to at some point), wash it cold inside out with mild soap or even just diluted white vinegar. Skip the machine if you can, soaking by hand is better for preserving color. The contrast you see on raw denim comes from the contrast between worn areas and protected areas, so it's exactly that natural variation you want to keep. So the less you wash, the better, but once every six months or a year isn't a crime either.