"I do not want to imagine it."
Translation:Ich will es mir nicht vorstellen.
The reflexive pronoun is in the dative case since there is already an accusative object (es).
NOW I understand! Thanks for this link - it's what a lesson on this ( & many other topics, I presume) should be. It'll probably take me a while to work through it, so Duo is going to have to wait! I'll look there for Modal verbs too - not doing very well at all on them with just Duo's exercises.
You can understand it by considering it literally, i.e., "I dont want to present it to me." Here "presenting to oneself" would be like "imagining ". In other languages too, like Spanish, a good example of this type would be "Me pregunto" which literally means "I ask myself" but really means "I wonder." You can see the similarity in meanings.
My excuses, this is a little rant. I was told that German does not care much for word order as declinations are used to show/know what is each word function in the sentence. So why is it that Duo does not accept: Ich will nicht es mir vorstellen. Would a German speaking person understand it?
They'd probably understand it, much as an English speaker would probably understand "I not want it imagine."
German word order is not completely free, so "does not care much" is overstating things.
You can rearrange some parts of a sentence due to inflections, but not others -- for example, verbs and adverbs have fairly fixed places in a sentence while nouns are easier to move around.
What are the rules for the placement of these adjectives and adverbs in a sentence? Why is the order 'es mir nicht' rather than 'mir es nicht' or 'nicht es mir' or 'es nicht mir'? Is it just something that comes from trial and error with no defined rules? I'm just guessing.
I think your question is a combination of 2 questions - one is the placement of the pronouns, the other the placement of 'nicht.' I'm not very good with the 'nicht' placement myself, although I remember that Deutsch Aber Hallo's a2 pdf discusses some of the rules for it.
Regarding the pronouns, check this out: https://www.thoughtco.com/sentence-structure-accusative-and-dative-1444619
"Das will ich nicht mir vorstellen", is this incorrect?
Yes. Using nicht mir sounds as if you don't want to put the idea into your own imagination but into someone else's imagination.
Also, personal pronouns such as mir generally come as close to the main verb (here: will) as possible.
Both leading to Das will ich mir nicht vorstellen.
Vorstellen means to present, not to imagine. In German, instead of saying "I imagine something" they often say "I present something to myself" (which basically means "I imagine").
The other thing you need to know is that word order is different in every language. In Spanish, for instance they would say "You are a person nice." But when you translate that into English, you should say "You are a nice person", because we put our adjectives before the nouns they describe instead of after.
In German, they always put the conjugated verb in the second position. Any infinitive verbs after that should go at the end of the sentence. For example, In English we say, "I want to go to Germany." "Want" is the conjugated verb and "to go" is an infinitive verb. So in German they would say, "I want to Germany to go." or auf Deutsch, "Ich will nach Deutschland gehen."
So this LITERALLY means: "I do not want to present it to myself." or a better translation: "I do not want to imagine it."