When choosing a rain poncho, it's important to consider several key features. Look for a poncho that is made from durable waterproof material, such as nylon or polyester with a waterproof coating. Ensure that it has sealed seams to prevent water from seeping in. Additionally, opt for a poncho with a generous size to provide ample coverage, and consider features like a hood with adjustable drawstrings, snap buttons or a zipper closure, and built-in pockets for convenience.