I usually do the opposite. I concentrate on a handful of well developed cities, infrastructure, and technology. Great for science and defense. Then, I come rolling out tanks to get the war machine in motion.
Usually, that's the best way, and start small. Hold your army back a bit a stock up on freighters with food supplies. This way you can quickly get your first wave of conquered cities up to standard.
For fast nukes without wasting gold, get a city surrounded by hills mined, railroaded, etc. for production. Don't ever worry about food there. With a granary and freighters you can quickly drop in food to grow, and every dozen turns or so have a city bring more food to prevent population decrease.
Just a few little tricks. Whats really dangerous is letting somebody be the Celts on large Earth map. Optional start for a perfectionist.
