Sitting down with a pad of blank paper and a pen and expecting to be struck by a flash of inspiration is the wrong way to begin your project. The invention process stems from thinking about a problem or inconvenience that you encounter in daily life and trying to solve it rationally. To begin with, go about your life as normal, but keep an eye out for problems that you encounter that you might usually bypass. Make a note of all the problems that you encounter and use this list to develop the possible inventions that you plan to build in your project.
Another way to approach the project is to look at inventions and appliances that assist you in daily life and think about how they could be improved. The important thing to remember if you do go down this avenue is that your planned alteration must be a radical one to gain credit in your project. If your alteration is only minor, it will be difficult to write up the development part of your project.
Experimentation and development are key to a successful invention. This is the area of your project where you can display your scientific knowledge and ability to apply that knowledge to everyday problems. Devise methods of testing your invention that you can draw useful and appropriate conclusions from. Test the invention on key areas, such as safety, ease of usage, effectiveness at completing the task and efficiency. Use these tests to hone your invention but never discard the stages you reach along the way. These can all be written up in the development section of your project.
Inventions are where the two worlds of science and commerciality combine. With this in mind, extend your project by examining different methods of production and marketing that could get your invention off the ground. This is where you're able to further display your ability to transfer theoretical science into the real world--an impressive attribute for a scientist.