When you first start playing, it can be tempting to spend your gold as fast as you can earn it, investing in workers and other such things. If you do that, though, you won't be ready for the impending enemy invasion. Make sure that you prioritize for walls and archers. A single archer won't do you much good, since shots often miss, so try to gather many archers and let their combined might turn adversaries into pincushions. Don't necessarily build towers for your archers, though, because then they won't want to go anywhere else.
