OK, so you decide to build up static defenses as soon as possible, and it looks like you're surviving, but then HOLY F*%#, an even more humungous enemy army shows up WITH ARTILLERY, wipes out your Towers and your army and everything else, so you throw your computer through the window.
Holy f*%#, you say, how is this possible? So you curse a bit and start again, and the same thing happens, and it happens every time. OK, so you've been playing the campaigns, and they seem pretty easy, so you try a custom game (CG) against the AI, and you're happily going about your business, and then, within seconds, it seems, a humungous enemy army shows up in your base and wipes you out. However, there are some aspects to this procedure that you will need to use and practice before you will be able to attempt to play against a real opponent. If the AI can freely roam the map, gaining experience and resources, you won't have a chance. Furthermore, the procedure described here can only beat the AI on certain maps - the small ones where you can contain it. There are some aspects of this that are just plain wrong for normal play, such as staying within the 40-population limit. Disclaimer: The 'advice' given here will only be useful for rank beginners, and completing the campaigns doesn't get you past that level.