I generally stick to remote spots that are free and are isolated enough to where I don't have to deal with lights or campfires from other campers. Also like to let my dog hang out off leash. The majority of these spots are down dirt roads with no cell reception so always have a good spare tire.
My current favorite spot in the Mojave in Granite Pass. 34.81408117699265, -115.61719375102717
It's a few thousand feet elevation and I've found it's sheltered from the wind more than most areas of the Mojave. Also has cell reception. You've got about a mile of dirt roads but it's doable by passenger car. There are seven or so dispersed camping areas, first come first serve and all of them have plenty of rocks and vegatation to block any light from other campers. I just spent five nights around the last new moon and I was the only person there the whole time. Little light dome from Vegas in the north west but not too bad. No services, pack it in pack it out.
The last year I've started to create little videos of each spot, including timelapses of the night sky from the cardinal directions. Here is Granite Pass
https://youtu.be/xBhKX96q3nwAmboy Crater is a popular winter spot in the Mojave, somewhat near Granite Pass. 34.557047592370644, -115.78112348990246
Little bit of light from Roy's Motel on Rt 66 but if you position your car strategically it's not a problem. You'll usually find other astronomers there around the new moon. Not a campsite, more of a parking lot for the trail head to Amboy Crater. There is also a large overflow lot just before the main lot. Bathrooms and picnic tables. So-so cell reception, paved roads.
https://youtu.be/i7EhoaZFl6wTrona Pinnacles - 35.61838683208204, -117.37361593931524 Pretty dark, awesome place to do nightscapes. Pit toilet but no other services. If you have 4x4 you can go pretty deep into the pinnacles to find a nice secluded spot. Bit of a light dome to the North from the town of Trona. Got about seven miles of washboard dirt road, doable in a passenger car but better in a truck. There is usually cell reception.
Panamint Valley - 36.08069657781777, -117.22202431285974 Just west of Death Valley proper but an hour or two closer. Head towards Ballarat and continue on Indian Ranch Road until you find a spot you like. Washboard dirt road for a few miles but should be doable in a passenger car. No reception or services.
For Death Valley I'll usually do Eureka Dunes dry camp. 37.11216903883487, -117.68091043216666
Best to have a truck or SUV with high clearance, you've got 10 miles of washboard dirt road. No reception or services but it's very dark. Free and first come first serve. There is a small campground with a pit toilet at the GPS location I provided. There are some more private turn outs a little further east down Eureka Rd but the road turns to deep sand quick after the first dry camp so be sure to have 4x4. This is the darkest site I've been to in southern California.
Another good spot in Death Valley is Mesquite Springs Campground. 36.9626809323363, -117.36767452942556 First come first serve and I think it's around $15 a night. Very dark, bathrooms, water, no cell reception. Easy to find a spot away from other campers and their lights/fires.
Grandview Campground in the Inyo Mountains is excellent during the summer. 37.33381950354476, -118.18762330659612
Also first come first serve, you should be able to find a spot unless you show up on a Saturday afternoon. It's at 8,000' elevation and very very dry so transparency is great. This is a popular spot and you'll find at least one other person with a telescope set up. No cell reception, accessible by passenger car.
https://youtu.be/clGNmVnkfgY