The first wave of Battlefield 4 Alpha Trial invites are being sent out today to randomly selected Battlefield players. The selection process is completely random, and though some might suggest that a high Battlefield Veteran status or BF4 pre-orders, this is simply not the case as the selection process is, once again, random.
For those that remember the Battlefield 3 Alpha trial, the amount of play testers will be increased as the trial progresses, so if you don't get an invite now, there is a chance you will get one in a few days or even next week.