I printed on card-stock the lyrics to the verses I wanted to learn that day, or you could just write it on the chalk-board. (But you don't want to always use one or the other. I like to mix it up with using pictures, words, chalk-board, actions... you get the idea. Just so it's different every week.)
Anyway, every now and then I left out a word and just had a blank. I had the missing words printed out and hidden in a bucket filled with macaroni noodles that I had left-over from something else. But you could do anything! Then one by one they came up and dug out a word and then had to find where it went. After each word we sang the song once through. Every time there was a blank I just hummed, even though they knew a lot of the words.
The key here is repetition. It always is! But the kids really like to come up and dig. It worked.