Historically, they announce in mid Dec for an end of Dec Ex DIV date. The run-up has always began in mid-Nov (so next week would be a good time to enter). You would want to long Jan Calls (so that you can benefit from the late Dec run-up) or short Dec Puts (so that they expire before EX DIV date.
Be careful playing with the Ex Div date versus the OpEx date for December. I think OpEx is the 21st and AGNC has been moving their Ex Div date earlier all year long. There is a reasonable chance that they'll declare an Ex Div date BEFORE Dec OpEx.