Well, you just have to change how you build and micromanage stuff.
Perhaps you should tell us what your economical strategy is. And on what difficulty you play on.
My strategy is making quantity cities mixed with libealism +1 production +1 culture + 1 happiness per city. I build them two tiles apart and actually get more than double the money from trade routes that i spend on road maintenance. Because i don`t build any buildings that cost maintenance (marketplaces i build) i have the city production open for any upcoming wonder. Whenever i need to build a new city i just buy a settler with gold.
Currently it`s turn 525 about 1000 AD and I`ve got over 10k gold, 7 cities, finished 5 wonders and 3 wonders still building. Altough i`ve built 0 monuments i am the 2nd on the lead in policies (Napoleon being the 1st).
This is on King difficulty. The strategy should work fine just about till the city happiness cost changes from 1 to 2 because of the difficulty level increase. I haven`t played the higher difficulties so i assume it will be harder to pull this off on say, immortal.