It’s best to have the longest telephoto lens you can afford. If money is no object, then you want the longest telephoto lens with the widest aperture that you are happy carrying. A wide aperture is helpful since it will keep your shutter speed higher, and allow you to shoot in lower light.
Serious wildlife photographers spend a lot of time learning about the species that they are after. The more you learn about the wildlife you are shooting, the better you will be at photographing them. Study their habits and traits, which will give you a better idea of what to expect. All of this helps you get amazing photographs. What time of day do they like to come out? Where are they going? How common are they?