Ways to use "don't give yourself away" (and variations of the phrase):
1. Your friend has a secret from her husband, and you fear her recent behavior might reveal the secret. You might say, "Be careful or you will give yourself away."
2. You and a friend are hiding from someone/something. Your friend starts to laugh or make a sound. You might say, "Shh! You are going to give us away!"
3. In poetry, musical lyrics, or other writing, the phrase could be used to express giving your affection/attention to a romantic partner.
Hope this helps!