Increase your training size, upgrading the barracks is the main way early on in the game, then build and upgrade armories also, 3 is the recommended amount but many players manage with just 1 or 2. Then as you unlock Ancient Wonders, there are several that are great for creating a good army. Needles of the Tempest means troops can be trained quicker, but this has a drawback of the barracks sat idle overnight (unless you can restart training with lack of sleep.
), and then increasing the training size more with the Dwarven Bulwark and Shrine of the Shrewdy Shrooms AW.
Squad size also comes into play as you progress, so it becomes a complex balancing issue, and then depends on your playing style. Love or hate tournaments, like to cater or fight provinces.
The whole game is a long SLOW game that can be played many different ways.