Thank you! I editted the tiles to take in your tips.

I've never been good at drawing deserts, so any other crits or tips are welcome.

It's hard to read. The tents and oasis stand out about as much from their surroundings as the individual sand dunes do. In other words, the objects have too little contrast and the sand has too much contrast (at least compared to the objects)

I think this tileset would benefit from removing the darkest colour on the sand, and darkening the middle colour a bit. Here are a couple of edits doing just that, as well as changing the overall values to be a little more evenly spread. I also made the sand less yellow because I think sand tends to be more tan than yellow, but that's more of a taste thing.
Alternatively, you could keep the sand as-is, and instead change the colours on the objects, perhaps like this. In this one, I cheated with the water and kept your colours, but redid the water surface so that it contrasts better with the sand around it.