Like the aspies above stated, as many as you can, at least 30. It sounds excessive, but theres a trick ive learned over time. Increasing your odds of a call back is number one. I call back the next day if the submitted application isnt too late in the day (before 2pm). From then on, ive usually taken the first job offer. If i get a 2nd or third call back while at the first, i keep note of it. They were interested enough to call, so theres a good chance that if the 1st doesnt work out, you can call back the others that showed interest before.
Despite how often this has worked for me, i still struggle with keeping my jobs. Im 32 and average 2-3 jobs a year. Though, i wasnt even disgnosed with HFA until i was 31. Im hoping now that with some knowledge of why i struggle i can hold onto my jobs a little longer.