This is a simple tip but one worth noting. The sound of shuffling feet in gravel, leaves, and dirt can often drown out the soft chip of a sparrow or chirp of a warbler. Walking softly is less intrusive on birds and enhances your ability to hear.
It also should be noted that “swishy” jackets, jingly car keys, or other noisy attachments to your birding gear can lessen the likeliness of hearing bird sounds. However, attaching your Duck Stamp to your binstraps, has no noise hindrance.