Having your needles break can be very frustrating and costly.  Try these tips to prevent this from happening:

1. The fabric may not be stable enough in the hoop.  Try rehooping your fabric, if that doesn't work you may need to use a stronger stabilizer.

2. The embroidery design may be too dense.  Scale the design to a larger size or try using a larger needle.  Remember that it is always a good idea to do a test stitch first to ensure that what you are expecting is what is being stitched out. 

3.  The thread may be caught on something.  Rethread your top thread and bobbin thread.  Ensure there is nothing in the way of the threads flowing off the spools easily.