Large, established trees should be first on your list as they are expensive to remove, expensive to replace and take years to become large enough to fulfill their purpose. Next would be trees planted in the last 2 to 3 years as their root systems are still not completely established. Normally, these trees would be first on our list as the larger, more mature trees are more drought resistant. However, sometimes a drought will be severe enough that even large trees may die or become so weakened that borers move in and take them out.
Next would be shrubs, then perennial flowers and finally lawns, annual flowers and vegetables. You probably see the pattern here. Start with what is most expensive to replace and move down from there. For more information on watering trees, see the last article in the June 7 issue of this newsletter at https://hnr.k-state.edu/extension/info-center/newsletters/2022/June7_2022_23.pdf (Ward Upham)