Best advice to newcomers, first build some farms, lumber yards, steel mines and quarry's outside town. Then some civilian houses and a hotel, so you'll have a general and some population to make soldiers from. Then use ALL your gold to get new resourses to buy soldiers (this should be done on day 3-5 so you'll have some defenses by day 7, when the enemy starts attacking, from here on you're on your own ;P
you need to be able to buy destroyed canons back, or upgrade the existing ones. Once you aquire tripple shot, the game becomes waaaaaaaay easier, this is both good and bad for the gameplay, it's nice to feel owerpowered but also it kills the gameplay because there is only one mission. but still 5/5 from me, great effort to make a great game.