In your example the negation follows 也, not the other way around. So I think what your textbook mean is 也 will never be after negation 不. In 我也不想这样, 也 is like the English word "either" as in "I don't want it to be like this, either." In another example 我也想吃鱼, 也 is like the word "too" or the phrase "as well" as in "I want to eat fish, too." "either" is for negation, "too" is for affirmation. But in Chinese, you just use one character for both, and that's 也. However, there is an exception to the rule you mentioned. For example: * 你不也想他回来吗？ Don't you also want him to come back? * 他不也是个男人吗？ Isn't he also a man? Here 不 is before 也, but as you can see from the examples, both sentences are rhetorical questions that have affirmative meaning but with a stronger tone. Extra examples to help you understand: * 这里的天空也是蓝色的。 The sky here is also blue. - 这里的天空也不是蓝色的。 The sky here is not blue, either. - 这里的天空不也是蓝色的吗？ Isn't the sky here also blue? * 他也喜欢画画。 He likes painting. - 他也不喜欢画画。 He doesn't like painting, either. - 他不也喜欢画画吗？ Doesn't he also like painting?

In the Chinese language，也 mean is ：also；too；as well as；as well. And 也 is a adverb. 1.也 express agree. for example, in this song: 王菲-我也不想這樣. 2.Sometimes it also can emphasize.For example，一点儿也不错。（ps:一点也不错mean is Indeed.） 3也 express transition. for example：尽管你不说，我也能猜到。(ps:Although you don't say，I also can guess it.) 4也 express we Tolerate or recognize a situation. For example：也罢（ps：alright！） My English is poor.Maybe I didn't express clearly.So If there's anything you don't understand the problems and difficulties, you can feel free to write and tell me.

I think you shouldn't believe the grammer rules, it doesn't always work well When you speak, you can use the word "也“ in sentence, or without "也”。“也” in sentnce usually just follow the previous sentence. Example: A: 我不爱吃饭 B:我也不爱吃饭。 Just express the same meaning plus "也“ after other person say something.