If you mean earning coins in general, you should visit the CookBook thread. It lists all the recipes and their full details so you can plan which recipes you should focus on serving to make the most coins. https://forums.storm8.com/showthread...STORY-CookBook
If you mean getting additional spaces for more appliances, you should be able to open an appliance slot every 4 or 5 levels you advance.
There's a chart that lists exactly which levels open an additional slot here: https://forums.storm8.com/showthread...l=1#post758470