I think that the "problem first" approach applies here. Rules like normal form weren't handed down from on high; they were developed as logical solutions to actual existing problems.
One key principle from a favorite article on teaching:
Coax into action the student’s mind to derive and establish all data which can be derived or established from the axioms or theories.
In application of this, I wouldn't even teach someone the normal forms as the first step. I would mention that there are different ways of structuring your relations, and that there are rules to follow which lead to a logical structure, and that we would get to them shortly.
The basic axiom I would teach is that each piece of information should be stored in only one place, so that it can't go out of sync (become inconsistent).
Then I would get some student interaction going and get the students to give examples of pieces of information they would keep track of. This PDF was my first introduction to database design. Borrowing and expanding an example from that, I might ask students: what information would they would want to track for a database of books?
Title and author are obvious. Some others will be mentioned: Page count. Publication date. Publication format. Publisher. How about "language"? ISBN.
Author's date of birth and date of death may be mentioned.
Writing these out across a chalkboard and start considering the matter further with a few examples and the huge number of problems with having a single relation will all of these attributes will become apparent:
What happens when a book has more than one author collaborating? What happens when multiple books were written by the same author, and then the author dies (and you have to update "date of death" in multiple places)? What happens when the same book was published more than once, in different years, by different publishers, with different formats and page counts?
Of course you wouldn't throw all those problems at them at the same time. But gradually, little by little, you could decompose that giant "BOOKS" relation into a database with all originally mentioned attributes, but in proper normal form.
And if you're doing it really well, your students would do all the normalizing, even if they don't know the rules they're following.
After any particular student suggestion (like making a separate "authors" relation to hold such information as dates of birth and death), I could then acknowledge it, validate it, and then present the general rule.
In short, rather than dumping data and explanations on top of them, I would get them to look and derive and establish the data for themselves, so they could really use it. Only then might I add additional explanation.