One of our recent discoveries has been how accessible Joshua Tree National park is from San Diego. Since San Diego is a popular place for conferences for Michelle's day job, we get the occasional chance to explore the desert and take every one we can.
Joshua Tree is a really large park! So the best way to see as much of it in a single trip is to drive to the south entrance (set your maps to the Cottonwood Visitor Center), explore a bit, and then drive up to the north entrances. There's more convenient food, housing, etc at the north end so you'll likely want to find a hotel or rental home up there. But if you only stay up there, you'll miss a lot of the park.
While you're at the south end of the park, take some time to hike the Lost Palms Oasis trail. Bring plenty of water and sunscreen no matter the season and if it's remotely close to summer, make sure to get an early start. This hike of 7.6 miles (3.8 each way to and from the oasis) has manageable elevation but some sandy trail makes it a bit more tiring than traditional packed dirt.
After the hike, you'll have a beautiful drive up to the north side of the park. Don't miss a stop by the cholla cactus garden. This short trail walks you through one of the only areas in park where you can see this species of cactus.
Pro tip: Don't forget to fill up in gas in Indio (if you're coming from the west). It's a long drive through the park without access to fuel. We found a gas staton a few miles past the entrance but would have saved a ton of time if we hadn't forgotten to stop.
How to get to Lost Palms: At the Cottonwood Visitor Center, go right on a dirt road. 1.2 miles down the road and you'll be at a parking lot for the hike. It's fairly popular, at least during busy days, which just adds another reason to get an early start for the hiking.