Tips,
1. You have to manage the growth of your population, it's mean everytime you grow your population you need facilities. More Facilities means more cost. So, the strategy is to keep your population balance, demolish the building that you're disliked, and rebuild them. You still can earn credits while upgrading without increasing cost.
2. Try not to sell raw item, but products. example, chair, table, vegetable, garden stuff etc. Selling it at low quantity but at highest price. Don't be affraid, people always need them but in certain number.