Often a kestrel will be found perched on a wire, which makes them easy to spot. But just as often, they will be at the top of a tree, both tall and short trees. So you scan the horizon and look for this shape at the top of a single bare branch and they can be spotted from a long distance when you know what to look for. This photo is cropped but I spotted him much further away just by the shape at the top of a tall tree.
Female American Kestrel (Falco sparverius )