最好 (had best / it's best to)

"Best you…" — strong advice

• best最好zuì hǎo = "had best / it would be best to" — a clear recommendation.
• you你nǐbest最好zuì hǎobreakfast早点zǎo diǎnto sleep睡shuì = "you'd best sleep early."
• Stronger and more direct than or / still还是hái shì…(suggestion)吧ba.

Subj + best最好zuì hǎo + Predicate

• best最好zuì hǎo gives firm, friendly advice.

you你nǐhad best最好zuì hǎoearlier早点zǎo diǎnsleep睡shuì。

• you你nǐbest最好zuì hǎobreakfast早点zǎo diǎnto sleep睡shuì = "you'd best go to sleep early."

Often warns of a downside

• The unspoken "…or else" makes best最好zuì hǎo stronger than a casual suggestion.

Recap

Read the full reference: HSK 4 grammar — Adverbs.