Quick tip: get better email engagement

I've been working on cleaning up my email list and getting better open-rates. One focus is to get better engagement. With the New Year coming, it's a great time for schedule changes. One thing I did was to send out a simple text only email and/or short SMS message asking people (segmented ONLY to those who have taken class at this time) to reply with their first choice for a class time change.
So far, we've had great engagement and response. It's easy for them and shows we want feedback. By replying to your email, it also sends a message to google and other email servers that the sending email is not spammy. Win/Win in my opinion.
What else do you do to increase your email open rates?

------
Here's what the email said:

Hello Rebecca,

As the new year is coming, it's the perfect time to adjust our schedule.

Would a 5:45pm start time fit better for you for the Monday and Wednesday evening classes (currently at 5:30pm)?

Simply let us know by replying to this email with your choice:

5:30p
5:45p

Thank you in advance as we work hard to support you every way we can.

Thank you for supporting our small, locally-owned studio.

With gratitude,

Jennifer Pahl and your Twist Yoga Family