Utilizing appropriate register and tone according to the context.

Have a clear understanding of the three primary levels of speech style in Japanese: polite style, neutral style and casual style. Their correct usage enhances the authenticity and appropriateness of your written communication.
Know when to use polite style (keigo), which comprises honorific, humble, and polite speech. It is generally used in formal contexts, including professional settings.
Recognise neutral style, also known as dictionary form, as the base form of verbs and adjectives. It is used in more informal, everyday contexts, but within the realms of polite speech.
Understand that casual style (kudaketa) is more intimate and represents a lower level of politeness. It’s used in friendly, casual situations or when addressing those younger or of lower social rank than yourself.

Develop an ability to discern the contextual cues that indicate which language style should be used. These cues may include the social status of the speaker and listener, their relationship, and the situation or environment.
Master the concept of ueno naka and soto, inner-circle and outer-circle, which plays a huge role in determining your language use.
Be aware of irony and sarcasm in written Japanese. Though these rhetorical devices are not as common in Japanese as in English, they do exist and can significantly change the intended tone of a sentence.

Familiarise yourself with various respectful expressions used when conversing with superiors, as well as humble expressions used when describing one’s own actions.
Expand your polite language vocabulary, which includes ‘desu’ and ‘masu’ forms.
Acquire a solid bank of casual language words and phrases. These might pertain to hobbies, daily activities or expressions of emotion suited for informal contexts.

Practice translating diverse English sentences into Japanese, paying special attention to matching register and tone to the original content.
Frequently read Japanese materials across various registers and tones to build familiarity. This can include everything from formal business letters to casual blog posts.
Identify mistakes in your written pieces and make necessary corrections, focusing particularly on inappropriate use of register or tone. This is key to refining your writing over time.