How do you differentiate between various types of voice-over work, such as commercials, animation, and audiobooks?

While there are some general distinctions between these three types of voice over, there's actually quite a bit of overlap as well. So it comes down to what they client wants. Some commercials require you to tell a story, like you would in an audiobook. Animation is all about character, which you might also have to do in an audiobook of a novel. So ultimately, listening to your clients needs and directions is the best place to start - regardless of the genre. If you need to, ask your client questions to ensure you know what they are looking for. It will save you time in the end.

Each project is different. For me, it´s very important to always ask the client what is the tone and intention of the voice they´re looking for, first.  As I record myself, I´m constantly reminding myself of those instructions. Sometimes we get saturated, specially in long projects. In these moments, it´s important for me to take a little time,  shake it off, and come back to listen to what I´m doing as if I were someone from outside, and confirm if it alligns with the concept and instructions I was given.

Every client has specific wishes. But as a rule of thumb, you could say, that commercials have to stick out and have to be different to be effective. For an audiobook, you tell a story and try to feel the emotions before recording something.

To practice, listen to a lot of colleagues and try to ask your clients if they have an example of what they like to hear.
Also, clients can listen in to hear me during recording, this takes a bit more time, but the recording will be accepted for 95% of the time as the client told you what to do and was happy with the result at that moment.

For commercials, an upbeat tone of voice is typically used, whereas for audiobooks, the delivery is slower and calmer, with frequent pauses to allow the listener time to absorb the information. For animation, the tone and emotion can vary widely depending on the character being voiced, covering a broad spectrum of voices, tones, and emotions.