Take a practice ACT and SAT test. Teachers need to prepare students for these exams and if you falter on a certain section of the mathematics portion, you know what you need to focus on yourself so you can better teach that material to others.
Enroll in additional teaching and mathematics classes at your local community college. This gives you the chance to not only learn more about your own teaching material, but also to analyze the teaching style of your instructors and see from a student perspective what works and what doesn't.
Meet with other match teachers on a regular basis to compare stories about your classes, look over recent test scores and trade teaching techniques that have proven effective. The best advice often comes from people in the same field since they have the experience to relate to what your own problems or challenges are.
Seek out workshops designed for teachers to assist with improving teaching techniques.
Talk to your students and ask them what helped and what didn't when they were learning a new mathematical principle. The students are the ones who can give you the most honest feedback about what is useful and what isn't when you are teaching.