1. Pronounce it Perfectly in Japanese
Hatsuon / pronunciation practice.
Get this done asap!
The longer one waits to speak Japanese correctly, the longer it'll take to understand it when heard. Plus, it's really difficult to figure out what foreigners are saying when they have poor pronunciation.
Second most important.
Get them off English alphabet as soon as possible.
Eg in english. They'll see zu and try to say it like an English word. Doesn't work. Wrong.
Use it to assist as little as possible.
Videos used to cost, but the government now releases basic videos and books free.
Go through the lessons.
Thoroughly practice common phrases and structures.
Eg. They don't need to know at first how to write これはなんですか。 これはーーーです。 But they need to be able to ask and respond to survive and progress.
Erin ga chosen goes through all the basics (1st year college), so it's good practice.
B. Sentence structures/grammar/particles
A. First 1000 words in Japanese
501 japanese verbs
This is the most critical to get past the beginner stage.
Even something simple like
"Is the bank open on holidays?" is impossible to ask until they learn "holiday" in addition to "weekday", "weekend", and preferably the major Japanese holidays.
B. 700 essential phrases for japanese conversation
+ basic grammar (eg barrons japanese grammar) and particles books.
They really need to drill in automatic responses for daily life.
E.g. A text book might say "Do you want to dine-in or take out for your meal?"
But in reality, you might hear it shortened to "takeout?" and need to respond. (Second most common that'll get learners stuck at the checkout is "point card?")
Particles say a ton, so no way around this.
Wa, ga, o, ni, de.... Learn them early on.
Verbs can be a little more complex, so that can extended into year 2-4+.
Present, past, future, progressive to start.
Mostly unnecessary today due to Google translate app doing pretty good, but in the long term to be useful as an adult, not tourist or spouse, a multi year thing.
Don't start with all the usual English kanji learner books - that'll mean they won't understand Japanese later on because they've missed out on years of meaning.
Sit them down with a basic grade 1-6 jyoyo kanji book like the Rainbow Kanji Jiten.
Isbn 4053009332 for my old copy, they have a new version.
The worst is when they learn from jlpt/English kanji books and everything's missing.
E.g. Why it's it sorted 愛案。。。 for 4th grade kanji? (There is a reason folks that kids in Japan learn it this way.)
Plus in english, the kanji 手 is often only defined as "hand" for learners.
They miss out on important uses Japanese pickup like 手術をする to operate on.
The missing mental connections for the language are tough to incorporate years later - best to learn them now and go slower picking up each kanji.
(Besides kids need 6 years for 1000~ so an adult trying to cram that in isn't going to learn well if they attempt 1-2 years unless it's a Full time job.)