When I was at earlier levels (now at level 52), I found that producing and selling wood was a good way of making money as it is quick to produce and 5 can sell for the max price of 100 simoleons. Visiting Daniel can be ok too as he often has good items for sale and at their lowest price, which you can then sell for the highest price.
But that's just me, I'm sure other people have different suggestions as well.
So far, I can't make money in the game. I don't understand how this is done yet. At the moment, I earn money for the game using best money making apps. I have downloaded several such applications at once, and by performing elementary tasks, I make a little money. Sometimes it can be up to ten dollars at a time. So I spend this money on building my city in the game. Sometimes I buy groceries at home. It turned out to be very convenient, I'm surprised. At first, I doubted it at all, but in the end, I was convinced.
