How to engage your core effectively
There are many ways to engage your core, but this is one of the most effective ones I know, The Restore Your Core method of core engagement involves using your breath to engage the deep core muscles. Here's how:
You can do this exercise in any position—sitting up, lying down, or standing. Bring your hands to your lower belly. Pretend that there is a birthday cake, and it's got 100 candles on it. Inhale. Exhale, and blow out the candles SLOWLY. This is what we call "candles" in RYC®. Try it one more time, and this time when you're blowing out candles, imagine that there is a golf ball moving from your pubic bone all the way up to your belly button, so you'll feel that engagement a little bit more strongly. That's called “up-arrow.”
I use these cues all the time in classes; in 1-1 sessions I can see whether you're really getting it right. If you practice these techniques you'll find that they start kicking in and your core will start engaging all the time when you're doing stuff in your daily life.
Here’s a quick video demonstration of candles:
Some other images that might work: You can imagine that you’re blowing all the seeds off of a giant dandelion (again, very slowly). You can also try hissing or humming. This video walks you through some other ways to find that sense of core engagement.