[spoiler]School is canceled, all young wizards are brought to hogwarts , the new boot camp for dumbledores army. Wizards will be give elementary training in DADA ,and special forces insertion into enemy territory.
Harry , being the seeker of Gryffondor will learn how to co-ordinate airstrikes using brooms and what ever that weapon that the ministry has.
The weasley twins will become the head of a skunk works type outfit, that will change from making prank spells and such , to full all out military charms and spells.
House elves will be recruited to form the new legions of the ministry of magic, making them the cannon fodder of Dumbledores army.
Legions of dragons, will be raised for the heavy bombardment squadrons and the muggle prime minister will have to become involved ,maybe even sanctioning SAS,RAF and RN support. Hopefully we will see some american wizards ,which so far has been limited to the quiditich world cup.[/spoiler]
One thing I think they are going to have to learn is that not all Slytherins are evil - they may not be the nicest folks in the world, but that doesn’t make them death eaters/voldemort supporters.
At the same time, not all Gryffindors are inherently good. A betrayal of some sort by a Gryffindor would be interesting. This doesn’t have to mean a spy placed in the ranks intentionally (I think the Sorting hat would keep that from happening), but a student who sort of…converts.
Snape and the DADA job: I’ve had this idea that Snape has had a prophecy (perhaps unknown to anyone else) that if he takes the DADA position, he will die in a final conflict that leads to the downfall of a powerful wizard. This could be Harry (yeah, right) or Voldemort. For that reason, he keeps trying to get the job knowing that it can’t happen until he has the job and he wants V gone. He’ll be the DADA teacher in the 7th book and will be killed by Daddy Malfoy.
I’ve got some other ideas, but I have got to re-read book 5 to help me put them into words, and that copy’s been out on loan for 3 weeks (and last time I talked to the person who has it, she was only halfway through it). Even then, I won’t have time to get back into it until after August 8 and the end of classes.