Rinse the 1 cup of glutinous rice until the water runs clear (4-5 times).
Pour rice into a bowl with 2 cups of water. Let soak for 4 hours or overnight.
Prep a steamer by bringing water to a simmer and add the steamer insert. Place a sheet of parchment paper or cheese cloth on top of the steamer insert.
Steam for 40 minutes.
Taste the rice for doneness. If it is undercooked, keep steaming for a few more minutes before testing again.
Notes
If you want to use a rice cooker, I would recommend using a rice cooker with a steamer basket and steaming the rice in the steamer basket.
Another thing you could do is test the sticky rice a few times in your rice cooker, so you know the exact ratio of rice to water. There are also nicer rice cookers with a sticky rice/sweet rice option in their settings which means it can cook sticky rice accurately. I would generally recommend a 1:1 ratio to start for sticky rice cooked in a rice cooker. Test out a batch and adjust accordingly. Add more water if the rice seems too dry or less if it seems too mushy.
Xoi should be stored at room temperature in an airtight container. If your home is too warm, place it in the fridge, and reheat for 10-20 seconds before serving. You will want to eat it at room temperature.