[BR3W CITY]

This might go long, but heres what I do to good result.
Washing:
You want to wash as little as possible, as over washing or over scrubbing can be just as bad as anything else for satin finish paint. The flipside of this is that anytime you get something oily or sticky on the paint, you want to remove it as soon as you can. Satin paint stains and ghosts a little easier than gloss because of the texture on the finish. To accomplish this, you need to use a good Satin soap, and it helps to use a spot cleaner.
Many generic "matte" soaps aren't any good. You need a soap that contains NO waxes or fillers of any kind. This means some people use everything from dish soaps, vinegar mixes, shampoos and other stupid crap. Don't. A GOOD satin finish soap will foam and work just like a "Regular" car wash soap, but will effectively clean the surface without leaving anything behind, a tougher task than it might sound. There are some natural type soaps that work well for this, and you don't have to dump half a bottle out to get them to work. I really like the products from Chemical Guys. They have a Satin finish soap that works really well for removing oil, grime and bugs, without being too harsh. While it might be a few more dollars than something from Walmart, if you put hard work into the paint, a few extra dollars is worth it. We use it on my Satin Cleared truck, as well as my buddies satin white PlastiDipped 350z to good result. It even works on vinyl siding. Both cars can be seen on my Youtube Channel, I can even dig up some footage of use using that soap through a Foam Lance on a pressure washer for the BEST no touch wash.
If you wash by hand, don't scrub and don't rub in circles. Start at the top, and use partially overlapping wipes, like you were mowing the lawn. Dunk the towel often, and use a dirt seperating bucket so you don't drag particles into the paint (you can build one cheap). Use a cotton towel or REAL microfiber or chamois. Avoid synthetics as they can scratch the paint. Don't use the towel for any other purpose.

Spot care and protecting:

Because of the issues with waxes and satin paint, people tend to think you can't protect a satin vehicle, and have to rely on washing for a good finish. This isn't really true. I picked up a satin Instant detailer from Chemical Guys as well (I don't work for them, its the only thing that works for me). It works partially like a cleaner, and partially like a regular instant detailer like is sold for regular paint. Using it on a clean towel helps pull off some grime and bugs without streaking, and doesn't rub a mess into the surrounding paint. Putting it on a clean surface removes dust or water spots, and does a nice job keeping the depth that satin paint can achieve.
There are also products now around that can be used to protect a satin finish much like a wax, but contain no actual wax. They are all spray on products, but they lay down a thin protective barrier keeping the body to the paint, helping water roll off and helping prevent dust from settling. They also fill the gap in between washings, and make it easier to spot detail after a trip, instead of being forced to re-wash every time. I have only had a chance to use a free sample of a product like this from two different companies. One from Chemical Guys and another from Croftgate. Both worked ok, and for the next spring season I plan to pick up a full size and see how it works for a full seasonal cycle.

Sorry for the long post.