/i/ and /e/ are both short, relaxed vowel sounds, so they are somewhat similar. To make the /i/sound, the tongue is down and relaxed in your mouth. Your lips should be relaxed as well, and be sure not to move them.
To make the /e/ sound, you should also be relaxed, but your mouth opens a little wider than it does for the /i/ sound.
Read these words to your student(s) and have them repeat.
For more pronunciation exercises, come in to pick up a copy of Pronunciation Fun! (Free for IC teachers and students.)