Winning the battle will raise the King influence even when the King does not directly involve. The King influence may go up faster if he leads the battle himself. Related to this, if he lose the land that he just capture, his influence won't go up or go up very slow. So make sure that you don't lose land.

Raid: also relate to the above, raid victories will not raise influence (or at least very slow). Raid means that you attack and capture an enemy province. You pillage then leave the province to the enemy to recapture. This kind of victory won't raise the influence since your King loses land to his enemy.

Alliance: don't brake alliance if you don't have to. Don't attack your ally.