Hi, your scores from battles depend on a few elements:
Happiness of your city
Points value of the enemy army
Points value of your army (has an impact if any troops are wounded/lost)
So if your city is enthusiastic you'll gain a boost to your score (which you probably noticed in the results board) normal happiness doesn't impact your score and an angry town will reduce your score. Beyond that each unit has it's own points value (found
here) and thus the score depends primarily on what you are fighting. To maximize points you need to fight high age and high value units and minimize your own wounds/losses (while using low point value/low age units) as you'll loose points according to your troop points.
Overall the equation would look something like this:
Battle points = (total points value of enemy troops - points value of damage taken) * city happiness bonus