The AI on the easiest difficulty is very easy to beat. Just play a skirmish on every map against an easy AI and this will pop in no time. Save up for heavy units, such as the Matriarch. Advanced strategies and tactics aren't really required against easy AI, just use brute force and you will overcome them in no time. Another method is to use an air rush, targeting nodes so that the AI cannot gain resources. Set the game resources to high and constantly spam dragons/choppers whilst upgrading your own nodes.