When the thread snaps, stop a minute and see if you can figure out why. Look to see if the thread has come off the spool and puddled around the spindle, or is getting caught somewhere else. See if it has jumped out of the uptake lever. If the thread is always breaking, get out your manual and double check how you are threading it. I've had several embroidery machines from different manufacturers and have always just used the 'normal' sewing tension, but I've heard that Berninas can be a bit fussier.