Shakespeare uses some good characterization techniques in Act 3, Scene 1, especially character interaction, to further present his main characters.
First, Benvolio is presented as the most rational character and the peacemaker. We see him being rational when he begs Mercutio to get off the street, warning that, "The day is hot, the Capulets abroad. / And if we meet, we shall not scape a brawl" (III.i.2-3). By interacting with Mercutio in trying to get him to go inside with him, he is trying to ensure that peace is kept in the city, in accordance to the Prince's proclamation.
Mercutio is portrayed as both impetuous and rash. Mercutio has no reason for wanting to stay out on the street; it is as if he is begging for another fight. He especially has no reason to be on the street considering that he knows Tybalt has challenged Romeo to a duel. If either of them get into another fight, they will receive the capital punishment of death. Therefore, Mercutio is being very impetuous and rash for not listening to Benvolio's warning.
Tybalt is actually presented as the gentleman in this scene. We see him behave courteously when we see him interacting with Benvolio and Mercutio by greeting them as fellow gentleman and politely asking permission to have a "word" with them (38).
In turn, Mercutio responds with snide, insulting remarks, even threatening Tybalt with a blow from his own sword, as we see in his line, "Make it a word and a blow" (40).
Romeo is presented as the character who most desperately wants to put an end to all of the fighting, especially since Tybalt and all Capulets are now his relations by marriage. He tries to walk away from Tybalt's threats and very honestly proclaims his love for him as a new family member, in his lines,
I do protest I never injur'd thee.
But love thee better than thou canst devise
Till thou shalt know the reason of my love. (67-69)
When Mercutio sees Romeo try to walk away from Tybalt's challenge, Mercutio again shows his impetuous, rash side by referring to Romeo's refusal as "calm, dishonourable, vile submission!" and challenging Tybalt himself (72).
Hence, through this scene, we learn a great deal about the characters through their interactions with each other.