The following sub-sections detail on the specifics of each keep on how to assault or defend them.  Below are general tactics and notes applicable to all.

General Notes

• Do not focus fire on trash NPCs (lower than sergeant level).  This is vitally important because healing warleaders and defilers will pick up massive aggro from healing then die from a thousand pinpricks.  If it's shooting/hitting the raid, it is far better for it to be hitting any other creep than a warleader/defiler
• Defendability for creeps, from easiest to hardest to defend, is TA > DG > TR > Lug > LC > Isen.  Keep this in mind when deciding if you want to stay and defend.  For the freeps it's TA > Ost > Lug > TR > LC > Isen.  The fast respawn rate of the FM's and Chieftains make taking TA a very hard operation when defended substantially.
• Assemble a rearguard when assaulting a keep.  It is important to prevent dead freeps from succumbing then riding back into the action.  BA's are critical in this force for their No You Don't to knock freeps off of horses.  Weaver Web the Earth also can slow horses till they are knocked off. 
• • Returning freeps should be killed either far from the keep or inside of it.  Those who die outside of the entrance or near a window can be rezzed from upstairs.  Keep this in mind when defending as defilers can rez those dead downstairs and create a powerful defensive force upstairs.  If you're attacking a keep, try to have a BA outside to keep minstrels in combat who try to rez.
• For a quick way to guage if you can take a keep given equal factors between freeps and creeps
  • PvE Force Required = Creep Raid Size - 2 * # Defending Freeps
    • Isen/LC:  PvE Force Required > 6
    • Ost/Lug/TR:  PvE Force Required > 12
    • TA:  PvE Force Required > 18
  • Note that these numbers fluctuate wildly based on the leadership and tactics of both sides.  With superior leadership and tactics, the creeps can beat an equal number  freep force in their own keep.  But for a typical PuG, this is a good first pass
• Unity of Command:  Coordination for both offense and defense requires everyone working together.  Do not be a hero.  Heroes end up dead.  Be a team player and follow the Raid Leader's orders.
  • On offense it is the Raid Leader's role to designate what stage of the attack the raid is on and to draw boundaries on where the raid shall operate.  Do not bite off more than you can chew and be purposeful on what group of NPCs you draw.
  • On defense it is the Raid Leader's role to keep morale up as well as keeping the intel flowing to all coming to reinforce.  Designate areas where to hold and when to fall back.  It is also the Raid Leader's job to call the final charge against the freeps or when to do quick assassination strikes vs targets up too far away from the main freep raid.  It is the members' job to hold tight and avoid being distracted until they hear the Raid Leader say go.  Being dead doesn't get you anywhere.  Stay alive until the attack is called then prepare to die while drawing as much blood as possible from the freeps.
• Boiling Oil complicates assaults on the entrance.  If there are no freeps guarding the keep, oil can be safely ignored.  Otherwise it requires the first creeps to take moderate damage (about 2k) upon entering the keep.  Reinforcements will be damaged and those retreating out of the keep will take another round of damage.  If an assault pushes into an oiled keep, they must keep running until they are out of the oil then stay inside as much as possible.  The tick damage after the initial is marginal.
• Sticky Tar is a LM skill which severely complicates the fight inside of a keep.  This will largely hamper creep melee.  Kill LM's inside to keep the amount of tar down and when a charge is called, a huge push must be made so that the freeps cannot pick off only one or two creeps coming through the tar at a time.
• Trolls are the mobile seige engines of PvMP.  They can take great damage and have good resilience.  Their damage is moderate and are stunnable so they are not very good offensively but are good at taking the alpha strike.  Use a troll to either pull NPCs out and deal with them, or to take the initial hits while the raid targets freeps or burns down individual NPCs quickly.  Another use is to charge the freeps with the troll for shock value while the creep raid is right behind it striking at vulnerable targets.  Freeps defending a keep near an entrypoint or window can be swatted out to either make them waste time running back in or throwing them into the creep raid for destruction.  Stomp is also useful to immediately stop any freeps with an AoE stun, letting them get run over by the creep raid.