I mean, you and your opponent both get 3 gold spots.
So, just use and protect your gold.
There are also 2 “neutral” spots out on the map, so you can move there.
They are away from your base, so usually you expand in that direction or put some kind of defense (TC, Castle) depending on the location.
You can grab up to 5 relics and store them in you monastery, that way you get “free” gold over time.
Last, you can go for the 3 gold spots from your enemy if they are exposed.
This could actually be your winning condition.
If they push you back, at least you got some of their gold.
For lategame (1v1), if all gold is out, you can sell on the market.
When the price is on the bottom (14), I would recommend to only sell food if needed.
Other than that, you can work on your spending.
Don’t get upgrades you don’t need, don’t buy on the market if not needed, think about army composition (so 1 gold unit, 1 siege unit, 1 trash unit instead of 2 gold units), etc.