I played conservatively to avoid running out of bingo credits. I always used 4 cards per game, but started with the lower-cost bingo games to preserve credits. As I gained confidence in balancing costs and rewards, I switched to higher-cost bingo options.
During my first week, I completed the dice-rolling side game hundreds of times due to the amount of rolls I earned. These side game rewards, along with credits, kept me afloat, and my balance slowly increased instead of depleting.
A key feature that helped with city progress is the card trading system. Most photos needed to complete a city can be traded, and I found it helpful to friend people randomly in the chat rooms from the list of people chatting. Some players would even hand out photos for nothing in return to those who asked, although for the most part you trade each others spares as needed. On some cities I barely had to play as I got handed so many spare cards, just from politely asking for them in the chat.