Enroll in music courses at an accredited academic institution related to composition such as music theory, ear training and instrumental techniques. A composition degree is ideal, but if you are naturally musically inclined, any music degree will teach you the music basics needed.
Take courses specific to video games and animation, such as Video Game Design, History of Animated Film or Animation Techniques. This will help you understand how your music will fit into the video game production process.
Hone your conducting skills with conducting classes and conducting everywhere you can (your church choir is a starting point). You will be expected to be able to conduct the music you compose so that it can be recorded for the video game company.
Write as many short pieces as you can in all orchestrations.
Hire musicians and rent out a recording studio.
Record your compositions.
Put your compositions on a demo CD.
Distribute your demo CD to video game development companies, along with your current resume.