-- Get Triple Arrow Weapon once you get $400 or close to $400. -- Save up for Cannon and Support. You should have cannon when the first knights appear. -- Try to upgrade Support to max and Castle until it costs $14000 -- Buy the Gun after Cannon.
Now, cause potential damage to your keyboard by button-mashing 5 & 6 once it gets tougher.
-- Buy the Chicken and Goat and/or Upgrade your castle to Max.
Now, button-mash 5 & 6, about every two cannonballs switch to 7 & 8, the go back to 5 & 6 once the chicken and goat are launched.
At this point you might want to invest in Meteor and/or Dragon.
Now you have lots and lots of money for repairs until you get swarmed.