Minecraft wiki entry for Powder_snow_farming, associated text: Powder snow accumulates only when it is snowing. However, sleeping resets the weather cycle, postponing the next snow time. Therefore, if the cauldrons are set up, the player should not sleep too often if they want to obtain powder snow, except for hopping in a bed periodically to prevent phantoms from spawning.
The requirements for powder snow accumulation is the same as ice formation: As long as the biome is cold enough to snow. Therefore, a good idea is to chain a powder snow farm next to an ice farm, so that both of these climate-dependent blocks can be farmed at once.
Some of the biomes do not snow on the surface, but they snow at higher altitudes. These biomes include the common-place mountains and taiga, the rare giant tree taiga, as well as all of their variants. Frozen oceans only snow at sea level in certain local regions, where there is normal ice covering the surface.
This means that if the player is going to stay in or close to a snowy or cold biome for a while, then a good option is to just set up the powder snow farm (as well as an ice farm) there. For a cold biome listed above, build a platform at higher altitudes where it is cold enough to snow, and place your cauldrons there. Powder snow will accumulate as long as the horizontal distance between it and the player is less than 128 blocks, so having a farm higher up won't affect its rates.