Always obtain permission before collecting seeds on private property. Ideally, seeds should be harvested within 100 miles of the restoration site. Target plants that naturally grow on sites similar to your restoration site. Do not collect seed of rare species. Accurate identification is important in order to obtain desirable species and to prevent collection and introduction of noxious weeds.
Most plants are easiest to identify when they are in flower.
Several books are available which can help you identify plants. Some are more technical than others. Unfortunately, many seeds are not ripe until long after the flowers have faded. This means that you must learn to recognize the plants based on leaf shape, typical location, overall plant shape, or fruit shape. Desirable species could be tagged during flowering in order to facilitate later identification.