To capture great images of wild animals, you might want to do some homework first. I typically do the following three before I head out.
Get inspired. Go to visitor centers and check out the bookstore. Flip through the photography books that have the images that inspire you. You can also do so online. A few of my favorite photo resources are Pinterest, 500px, Flickr. Or simply google the topic and see what images you’ll find.
Understand the right time and location to photograph wild animals. Ask the staff at the visitor center where in Yellowstone exactly you can spot wild animals, and what is the best time. Yellowstone (and many other national parks) is huge, you can spend a whole week driving inside the park. But you won’t see animals everywhere. Lamar Valley and Hayden Valley are what we learned the best spots to photograph wildlife. However, with a bit study, you might find that Hayden Valley is not car accessible. If you really plan to go there, make sure to budget the time to hike into it before the “right hours”
Optional to sign up a ranger tour. Although we are very lucky to see many wild animals ourselves, if you want to maximize the number and type of animals you see due to limited time, do a ranger tour. The caveat is that most rangers will restrict you to keep a big distance from the animals for security reason, this means if you don’t have a powerful telescope lens, your animals will appear small in your image. You can certainly use the ranger tour as a starting point, and do the “deep dive” later yourself, if you have more than one day in the park.