Choose an idea that really interests you. Break the idea into pieces and concentrate on the pieces that you are least confident that you can do; these are the "make or break" components. If you cannot solve these, then your entire solution will fail. For example, if you have an idea that depends on a hardware sensor that you need to wire up to an Arduino board and in turn connected to a computer, but you're not confident in how to get and analyze readings from that sensor in real time, then that is a make or break component.
In order to demonstrate that you can "solve" the component, develop a proof of concept—a bare bones demonstration of the component working. In this case, it would be a simple program running on your computer that polls the sensor and reports the raw readings.
Be ready to demo a PoC any time up to and including the day that this assignment is due.