When searching for stock photos, use multiple keywords in your search. Instead of a single-word search term such as “flower,” try “summer flower,” or instead of “family,” try “family portrait.” You find more options specific to your needs with less searching.
Look for images that you can use multiple times and in different ways. If there are two versions of a photo, go for the full-frame version so you can crop it yourself based upon your image needs, which allows you to get more use out of that single image.
Use a search engine for photos across multiple sites instead of looking within one specific website.