Diplomacy is a facet of War of the Avatars that's easy to overlook, but it should be a cornerstone of your strategy. Talking to other players, trading information, giving gifts to other realms, and so on, is a very cheap way to extend your influence in the campaign. Your goals, both immediate and long- term, can be accomplished much more easily if you have allies to help you out.
Talk to other realms in your neighborhood; you may have mutual interests and goals. Don't forget that the Savage Frontier is full of friends and foes alike!
Forging a formal alliance with another realm is a great way to get ahead. You can intimidate other realms into either joining you or going off to seek easier targets, and otherwise win friends and influence people. Since the players in an alliance can all win a campaign together, an early alliance could last for the entire campaign. But all this happens only if you avail yourself of the chance to talk to other players!
Don't forget that having your units under either a Conflict or Explore order sends out clear diplomatic signals. A Conflict order causes your armies to attack anything they meet, which definitely marks you as hostile. An Explore order, on the other hand, tells realms you meet that you're willing to talk to those around you.
Orders that can serve diplomatic purposes are Ally, Announce, Assign (you can give items to other realms with this order), Conflict, Declare, Explore, Give (gold), Inquire, Oppose, Proclaim, and Seclude. The descriptions of these orders tell you how to use them. Neglect them at your peril!
Diplomacy Example: The Destiny Shields player decides to Proclaim himself on his first turn Order Sheet: PROCLAIM. Since all realms start out secluded, issuing a Proclaim order enables other realms to get your address with an Inquire order once they have encountered your realm. Without this Proclaim order, any player who Inquires of the Destiny Shields player's address receives only a "This realm is secluded" reply.
By his fourth turn, the Destiny Shields player has bumped into four realms. He
decides to send a Declare message to these players: DECLARE ALL "I'M NEAR
ZUNDBRIDGE. LETS ALLY & STOMP HOSTILES." In this message, he gives his general
location and briefly asks these realms to join with him in getting rid of the
computer-controlled forces in the local area. He figures the risk of announcing
his location is worth it if at least some realms go in on this cooperative
venture. He also establishes himself as a ruler willing to talk to others, not
a bad reputation to have in this game.