1) Before the event begins and you intend to be online, you must send 100% of your own troops out of your city to reinforce allies. Do not keep a single troop at home for defense. I suggest finding 3 or 4 people that you can all exchange troops with.
Points breakdown:
You get points for city surviving a wave (not as many points for troops getting kills at your own city). If you leave troops at home, people reinforcing you will get very little points.
You get point for troops getting kills while reinforcing allies.
2) Do Not Heal Troops During the Event: When troops are healed in the Hospital, they are immediately returned to your city. This violates Golden Rule #1 and will cause your troops to steal kills from your allies. If you absolutely must heal to better help your allies, be sure to heal them and quickly send them out to reinforce.
3) Fortify Your Guard Station: Go to your city's "Guard Station" and assign your three strongest heroes. DO NOT use those heroes on your marches to reinforce allies.
4) If someone that you are reinforcing is defeated twice (burned twice) then recall all your troops and send to another player that is still not defeated.
Notes:
Shields Are Useless: Peace shields (bubbles) do not protect you from Viking attacks.
No Resource Loss: You will not lose any resources if your defense fails
Reference: https://kingshotguides.com/guide/viking-vengeance-expert-guide-beginner-to-advanced/