Manual battles obviously.
Best fleet combo I've found is three large warships (the ones with the 2 chevrons), and two small warships. The three larger ships are interchangeable but the two small ones should be the frigates, the fire arrows and reload is pretty help full. There is also the grenade which is on the gallon i don't recommend this one because of the splash damage can cause friendly fire.
The tactic i used was to capture the enemy ships. It's pretty easy plus you can gain tons of free ships this way. This will also help count towards the your vessel, my vessel achievement.