I take FLVS World History and I actually just finished a DBA yesterday haha ;p
Some of the things I prepare and think about before taking a DBA is look through the "possible topics" page that is at the end of the lesson titled "Module Review and Discussion Based Assessment"
I also quickly skim through each lesson just to pick up on some of the stuff I might have forgotten while studying.
You should also remember that your teacher calls so many students before you so he/she would probably be lenient if you do bad. I've done really bad on a World History DBA once and my teacher let it slide and let me progress instead of rescheduling a DBA. So just relax when you take the DBA.
Also if you have any note on your computer or on paper you are allowed to have them out during a DBA if you need them.
Hope this helps, let me know if you need any more help I got u
