Start by using your radar view to check your opponent's turret layout and search for weaker areas. Evaluate all the lanes can be used to deploy your boats and select the ones that offer you an advantage. Avoid double fire and try to get as many Jade Barrels as possible. Expend all those Jade Barrels during your attack because they are not saved afterwards. Keep in mind you do not have to deploy all your troops at the same time. If necessary, deploy some troops to flank your opponent in order to eliminate turrets. When safe, deploy one ship in the middle lane to get Jade Barrels. Always send in your entire fleet. Surviving troops will be returned to you after the battle ends.
Diamonds
Instead of spending diamonds to speed production early in the game, save them for more difficult situations later. Complete missions and watch advertising videos to get diamonds.
Upgrades
Start by upgrading buildings that generate resources, especially gold. You will need gold in order to attack, and it is not earned during battles.