Best advice: don’t worry too much about this test. The Advanced test requires a lot of knowledge and experience, but this Rapid developer test is almost too easy. After a couple of weeks of doing learning paths and creating some basic apps by yourself and having basic data design skills, you will do fine. And there is (at least a couple of years ago) no time limit so you can browse the docs.mendix.com to find your answers. Good luck and make your badge color change soon.
Here are some customer stories. Maybe you can use this to create some exercises yourself.