I would like to say “you first” in Latin. With all the different ways to say you (tu/vos....I can’t remember it that well from school)....with the correct corresponding first.... Thanks so much!!!!
I would paraphrase "You first" as "You are the first" or "You must go first". In the first case, "the first" is a predicate. A nominative case could be used. In the second case, "first" is an adverb.
Primus means "first" and is a first declension adjective. Primum is the adverb form.
If singular, the possibilities are: tu primus, tu prima.
If plural: vos primi, vos primae.
In the comments on the other answer, I think we've concluded that you could use "tu primum", "tibi primum", or "te primum" depending on whether "you" is the subject, beneficiary, or object of the implied action, or you could say "sis primus" (to a man) or "sis prima" (to a woman).
In the plural, these would be "vos primum", "vobis primum", "vos primum", "sitis primi", and "sitis primae", respectively.
There is no tu or vos with the adjective since in that case the subjunctive mood must be made explicit by including the verb, and once the verb is explicit, nominative case pronouns are redundant and omitted.