There isn't too much to know about racking rules in nine ball, except that you are required to place the 1 ball at the apex of the rack and the 9 ball in the center. The rest of the balls do not have to be racked in any particular order — at least not according to the rules. Some players use a diamond-shaped rack, but you will find that the higher level players much prefer to rack the balls in a diamond shape within a regular fifteen-ball rack because they can more easily place their fingers inside the rack to freeze the balls. Some diamond-shaped racks leave no room for you to tighten the balls with your hands.
After you've read about the strategy of the break shot, you will want to try a few racking techniques of your own. In nine ball you will typically rack the balls for your opponent, so there are a number of things you may want to consider in terms of position play — like where to place the various numbered balls so that consecutive numbers may wind up on opposite ends of the table after the break.
Table layout for opening break in nine ball. The 9 ball must be in the middle.