Teaching birdies new words?

I have two atiels, both of them say three words and phrases. One of them was taught in the shop I bought him from, the other learned from the first one lol! How do I go about training them more? Is it just a case of constant repetition or are there other things I can do? How about leaving a tape of my voice when I go out, or will that just annoy and bore them after a while?