There is numerous test prep online available to practice for the instrument rating theory exam. Gleims has always been popular among pilot students to study for theory exams. But there is also test prep software by Dauntless Aviation. Using Gliem's test prep books to study and the Dauntless Aviation software to practice answering the question. Using the dauntless test prep, you will get used to answering multiple-choice questions answers similar to the actual FAA test. Once you practice using dauntless test prep, the actual test will not seem unknown. Set a time limit and use the dauntless software to answer questions and see your score. You will be ready for the actual FAA theory written exam. There is an article here about IFR written test preps.