Does the play progress steadily from the beginning or does it open with some event?

The drama does progress steadily beginning with Act 1, Scene 1, when the Weird Sisters plan their meeting with Macbeth.  The first witch asks her sisters when they will all meet again, and the second witch states that it will be after the battle is over; she is referring to the battle in which Macbeth is fighting currently.  First witch wants to know where, and the second says they will meet on the heath, and the third says that this is where they will meet with Macbeth.  In the final lines of the scene, they chant, "Fair is foul, and foul is fair," implying that, at that point, what seems good will actually be bad, and what seems bad will truly be good (1.1.13).  Macbeth's transformation from a loyal and true friend and kinsman to the king into a treacherous and traitorous murderer is initiated by his meeting with the Weird Sisters, but their planning of this meeting (as well as the fact that they seem to anticipate manipulating Macbeth) in the first scene helps to ignite the drama right away.