Defending a keep is rather simple. Defending a keep will take significantly less players then attacking a Keep would. Actually if you had a good Bright Wizard and Warrior Priest you could easily hold off a whole attack force. (Same goes for Sorcerer and Shaman)
The main thing you will need to do while defending a keep is to get some Oil up to fend off the attackers asap. The big can of Oil is the bane of the opposing realms existence. Without the attacking teams healers on their A game two Oil spills will wipe almost everyone at the front door.
Once you think they are going to bust down the Outer Door (Say it's at 20% with no oil up.) Destroy the Ram pad close to your Inner Door and fall back inside the keep. Throw up a new Oil and Rinse and repeat the process.
If they manage to bust through your Inner Keep doors, then it's time to organize yourselves and attack their main tank and healers. The extra damage of everyone on the main tank will be enough to take him down. It would also be a good idea to put some pressure on their healers. They can't heal themselves and the tanks at the same time!
Tips & Things to keep in mind
- If you're a healer rez the dead! You need every person you can get to help, don't discriminate rezzing someone just because he is retarded. Because he can be a retarded meat shield! =D
- Always make sure someone has the oil up, or is on the oil. The oil is the #1 thing that can prevent anyone from taking the keep. On the same note make sure that the enemies don't sneak through your postern door and take out the oil.
- Destroy the outer ram pad if you know your keep is about to be under attack, same deal with the inner ram pad.
- If a lot of people are dead, always rez the healers first, more healers alive means more rezzes to go around.
- Always make sure you have at least two Oils on you before going and defending a keep.