See the Mirror Phenomenon during the rainy season between January and February.
The main thing is to bring water and a raincoat. Also, toilet paper and small cash. Don't forget your camera and comfortable shoes.
It is recommended to walking slowly and stopping to rest. Also, sleep well, eat light, and avoid alcoholic beverages.
Bus from Potosí to Uyuni. Night bus from La Paz (12 hrs). Train or bus from Villazón, near Argentina.
Accommodation quality may differ from cost. You can book online, but I recommend bringing cash for lodging.
Affordable option: The best way to hire a Salar de Uyuni tour is directly when you get off the bus.
You can also book tours online and choose something more high quality.
You will be 3 days exceeding 3500 meters above sea level. Therefore, my recommendation is that you go with travel insurance.