Don't have any more unit in cities than you have free upkeep slots unless you have money to burn, and if your losing too much money, disband any non-free upkeep troops you do not absolutly need. Strictly speaking you need eithier 1 or 2 armies ealy on. 1 to guard inside your borders, and one to go on the attack. If necessery, disband your attacking army until you get enough income to afford to keep it.

Likewise, don't have a bigger navy than you need.

Lastly, get as many trade agreements and ports up as you can, they give at least half my income normally.