To explain using your sentence:

“Didn’t you slowly brush you hair with the special brush I bought you yesterday?”

can be translated in

“Ne t’es-tu pas brossé doucement les cheveux avec cette brosse spéciale que je t’ai achetée hier ?”

This is a question, so the subject goes before the verb “es-tu ?”

Brush is in french a reflexive verb, so it becomes “t‘es-tu brossé ?”

The negative “ne … pas”, “ne … plus”, “ne … jamais” comes before and after the verb and before the participle past (“tu ne t’es pas brossé”), but it’s a question so it’s after the subject too: “Ne t’es-tu pas brossé ?”

Slowly, as an adverb, can be placed before or after the participle past, it doesn’t matter but a common thing is to place it after: “Ne t’es-tu pas brossé doucement ?”

The direct object usually comes after the verb (or the participle past) and the adverb: “Ne t’es-tu pas brossé doucement les cheveux ?”

The way comes usually after the direct object: “Ne t’es-tu pas brossé doucement les cheveux avec cette brosse ?”

But which brush ? The one I bought you yesterday. You have to place it just after the brush. And the verb “avoir” as an auxiliary verb (don’t know if the term exists in english, in french this is called “auxiliaire”) has the same gender and number as the direct object which is “que” in “que je t’ai achetée” because the direct object is before the verb, and “que” is the brush, so it becomes: “Ne t’es-tu pas brossé doucement les cheveux avec cette brosse que je t’ai achetée hier ?”

This is like a new sentence: subject first, then reflective verb but the “que” goes before to introduce the sentence, it’s like a concatenation of “Ne t’es-tu pas brossé doucement les cheveux avec cette brosse ?” and “Je t’ai acheté cette brosse hier” (here, this is “acheté” and not “achetée” cause the direct object is now after)

Hope this is clear, but explaining it is a bit difficult, the place depends of many things and sometimes it’s idiomatic !