Then start disbanding your armies.

With factions that begin with a large military (for example: HRE campaigns), priority no.1 should be the disbanding of armies that aren't likely to face a threat in the near future. That means any inland city garrisons should be chopped to a bare minimum and your building priorities should be the Barracks buildings in order to get the free upkeep units. It makes a huge difference at the start of the game. Once you've done that, concentrate on farms, roads and trade. Its unlikely you'll need an army bigger than 5 units for the 1st 10 turns.