Match curriculum carefully with what peers in your state will be learning. Don't shy away from categories because they prove difficult or time consuming. This will help you on standardized tests and for testing out of classes.
Keep careful records of your studies. Record what textbooks were used, outside courses taken and any extracurricular activities.
Enroll in online high school or college prep programs. Get in communication with your local high school to see what online classes and credits they accept. Search for programs that support the textbooks you selected to use.
Look for classes to test out of, or packets for credit hours. The majority of classes have tests that can be taken to get credit for the class, without having to take the class. Packets are also available for a wide variety of credits.
Study other successful homeschool strategies. Lots of books online offer ways to get acquainted with the homeschool system and earn high school credit for your efforts.