The same way you gain honor in M&B for V 1.011 or Warband - you do quests for lords successfully, you fight bandits for peasants in the villages (fetch grain, fetch cattle, teach peasants to fight, etc.) and refuse a reward for it, you capture lords and release them after battle without charging ransom, you do quests for Guildmasters successfully, like the one where you have to persuade two lords to agree for peace, and decline to accept the reward for doing it. Or, you track down the murderer for a lord and refuse to take the reward.