You ought to regulate your manner of behaviour towards others, not according to your own humour, but agreeably to the pleasure and inclination of those with whom you converse.

[Il che acciò che tu più agevolmente apprenda di fare, dèi sapere che a te convien temperare et ordinare i tuoi modi non secondo il tuo arbitrio, ma secondo il piacer di coloro co’ quali tu usi, et a quello indirizzargli.]

Giovanni della Casa (1503-1556) Florentine poet, author, diplomat, bishop

Galateo: Or, A Treatise on Politeness and Delicacy of Manners [Il Galateo overo de’ costumi], ch. 2 (1558) [tr. Graves (1774)]
    (Source)

(Source (Italian)). Alternate translations:

It behooves thee, to frame and order thy maners and doings, not according to thine owne minde and fashion: but to please those, with whome thou livest, and after that sort direct thy doings.
[tr. Peterson (1576)]

You must know that it will be to your advantage to temper and adapt your manners not according to your own choices but according to the pleasure of those with whom you are dealing and act accordingly.
[tr. Einsenbichler/Bartlett (1986)]