How does Shakespeare build suspense in act 1 of Romeo and Juliet?

The opening prologue of the play does a nice job of setting the stage with tension and suspense. The third and fourth lines of the prologue alert readers to the fact that the general setting involves two warring families.

From ancient grudge break to new mutiny,Where civil blood makes civil hands unclean.

He uses words like "grudge," "mutiny," and "blood." All of those are not pleasant or happy words. Shakespeare ups the suspense in the next four lines by telling readers exactly what is going to happen to the two young lovers. We know from the beginning that they are going to die.

A pair of star-cross'd lovers take their life;

This is incredibly suspenseful because we immediately start wondering why and how and a whole host of other questions regarding these deaths.
After the prologue, Shakespeare continues to set the stage for a suspenseful play by having the opening scene be a violent scene. He has the Capulets and Montagues throwing insults at each other until the situation escalates and turns to actual violence.
Scene 2 shows audiences that Paris is trying to marry Juliet. Audiences know that the play is titled Romeo and Juliet and Paris is not part of that title. Shakespeare has introduced a possible love triangle quite early. All of this serves to raise the suspense level for audience members.