Right now, you earn money each real-time day (you don't need to play every day, it adds up to 10 days). You can also use a debug option to get more money. There's currently a glitch that crashes the game if you use this option on a new character though... So for now if you want to use it, save your game and reload the save first. I'll get it fixed asap.
Later on, I'll add more options to earn money, like achievements to increase the base income or minigames. The first minigame will most probably be related to the grocery store, but I'm not sure what form it'll take yet.