1. Your fretting technique needs to be just right, so each note is clear. Pick each note in the chord one at a time to make sure, as it's very hard to hear the difference between playing it correctly vs incorrectly if you're strumming the whole chord.
2. Your strumming needs to be even across all the strings. Many people play the thicker strings quite hard and the thinner strings quietly or not at all, but if you can get the thinner strings to ring out too your chords will sound more balanced, so it's worth practicing strumming with even pressure all the way through. You can even exaggerate the thinner strings to get the idea.
3. Make sure your setup is good, with your guitar in tune and a suitable distance from your microphone (not too close so it overloads), and with the backing music not too loud. If you're having trouble hearing the backing music then headphones can work well.
See the video how to play it correctly: Getting Em & Am Correct*
*Video includes footage from GuitarBots.