I'm currently a high school senior and I'm applying as a music major for colleges (not as a music educator though); however, I have spent a lot of time talking to my music teachers and college professors about their career choices.
The most important questions I think are; who do you want to teach, what do you want to teach, and what can you currently work on that will help you in your future?
Are you looking to be a private music instructor, or a teacher at an elementary school, middle school, high school, or college?
If you are looking to be a private teacher (assuming you are a woodwind player) becoming proficient on your instrument and common doubles is important. If you know how to play the saxophone, learn how to play the flute and clarinet. This will open you up to more performance and teaching opportunities if you're interested.
For whatever you intend to go in for in college, piano proficiency is a requirement. Becoming familiar with the piano as early as you can will save you time and money later on down the road. Take a theory course if there is one available and start developing your ear. There are plenty of apps and website devoted to helping with the recognition of intervals, progressions, chords, and so forth. Being able to recognize good intonation is a necessity.
If you are looking to be a grade school music teacher, familiarize yourself with the different programs that schools teach that are music related and familiarize yourself with the different instruments that are used in the courses. At my school, there is a full orchestra, chamber orchestra, three different choirs, an AP Music Theory class, two concert bands, a marching band, jazz band, and a color guard class. The director of music at my school is personally involved in most of these programs in some way. I'm pretty sure student teaching is a requirement for a music education major, which will require you to work under a music teacher at a school. Be prepared to teach and work in classes you may not have initially wanted to work in. Flexibility goes a long way.
As for applying to colleges, it straight up sucks. It is time consuming and application fees can get hefty depending on the amount of schools you apply to and whether or not your financial situation allows for you to have the fees waives. If you apply to a school that is not strictly or primarily music orientated, you will be required to fill out the regular school application as well as the music supplements. All of the schools I've seen have required an audition in addition to other stuff that varies depending on your major. I agree with finding a school that focuses on education rather than performance. Do your research on schools and find an environment that you think you will work best with. Smaller universities or programs will offer you better communication and relationships with your professors. Larger schools may have small music programs which will offer the same type of relationship with your teachers. Talk to music educators that you know and ask them about their experiences and connections. If you are interested in a specific school, email some of the professors. Many of them are very good at answering questions you may have and responding to emails. There are plenty of websites like collegeprowler that will give you reviews on the social aspects of a school. Don't get caught up in heresay or hype. Determine what will work best for YOU.