It hardly rains in Israel so there is no use saving this museum for a rainy day. The vast collection of art, archeology, sculptures and antiques can easily keep one entertained for hours.
I definitely recommend beginning with the Model of Jerusalem followed by the exhibit devoted to the Dead Sea Scrolls.
The sculpture Garden goes along the outside of the museum and is often overlooked yet is extremely well done. There is even a Botero sculpture, making this bohemian very happy.