Hot water in the wash and a dedicated microfiber detergent like Chemicals Guys sells. Hot water will help the fibers expand and release all the junk they hold onto. Dry on low with no fabric softener. My expensive plush paint only towels get hung to dry and then put in the dryer for a few minutes afterwards to fluff them up a bit. It can seem silly to take the extra steps and use a dedicated detergent, but it makes a huge difference in how clean they come and how long they last.

OK dammit - based on all these responses I just went out and replenished my microfiber / drying towels vowing to NOT wash any of these in the washer with my clothes but to friggin' hand wash them like girly unmentionables. I AM however going to keep washing the tire/horrible towels with my clothes.

Oh god why

Why would you want to fill your microfiber with lint?

I solved this problem by buying enough towels that I can wash all 3 of my vehicles on the same day. No problem with having enough dirty towels to justify a separate load.

I always run a rinse with a cup of white vinegar through the washer (rinse cycle) before doing a load of detail towels just to make sure that the fabric softener my wife uses is out of the washer before I begin. Then I use a microfiber detergent and an extra rinse cycle (with vinegar). All my towels are then air dried. If you use a dryer you may be inadvertently exposing your towels to fabric softener as it tends to build up inside the dryer. This may all be a bit more than most do but my microfibers are all holding up well.

Inspect before use
 

I also inspect my microfibers under strong light after washing / drying. Sometimes notice a couple of places where a bug's body part or piece of semi-hard crap is stuck inside the fibers. I pull them out with a pair of tweezers before using them. Despite the thick fibers it only takes one tiny piece of hard crap stuck to the microfiber to scratch the finish.

I have MF towels that cost more than my clothes so yea they get special treatment.

I keep them separate and wash them separate:
drying towels
wax towels
interior and glass towels
exterior (wheel) towels

I washed my wax towels with a drying towel once and then it wouldn't absorb water anymore, so now everything gets washed separate.
Like others have stated, hot wash, vinegar in the rinse, low heat dry with NO fabric softener.
Then they all get put away in plastic totes so no dust or anything can settle on them.

I wash 'em as I dirty 'em. If two get used, two get washed by themselves in the washer on warm/ hot water with their own detergent. Towels with heavy build up of polish or wax get hand washed first to remove some of the build up and maybe even sit in a bit of white vinegar before going into the washer. My towels are more precious to me than my clothes, so yeah.

I believe one episode on ammonyc said to keep your wash separate. this is to prevent knots from building up in your microfib and drying towels. these knots will produce scratches and uneven finish when you eventually go dry/wax your car.