Find a room large enough to meet the following requirements:

A. there is no ventilation equipment, or the ventilation equipment can be turned off.

B. there is a stable heat source to provide updraft.

Step two:

Improve the indoor humidity, that is, spray water like in the video.

Modification: It is worth noting that the indoor humidity is almost saturated, and the water is sprayed only to further improve the local humidity, and the water will soon fall to the ground. According to the previous conditions, water evaporates from the ground and there is an unusually slow upward airflow, which provides excellent conditions for the next step.

Step 3:

Release condensation nuclei. I don't know much about what the material means, sawdust. Flour? As long as the particles are small enough, there should be no problem. It needs to be ejected under a certain airflow and fully combined with water in the air to form a cloud.

The key to cloud formation is cold air. Even in relatively dry air, a few condensed nuclei will form clouds when they meet cold enough air. Indeed, the temperature factor is ignored. There should be cold air in the third step. In fact, the most important thing to consider later is how to ensure the stability of the cloud. If you simply make a cloud, an air humidifier should be enough.

Besides, lighting is very important.