Instead of lecturing my students on function notation, as I used to do, I now start each class with a mini-lesson (15-20 minutes in length) to go over just one or two examples of what they will be learning about today.
As soon as the mini-lesson is over, I set them to task on this worksheet, which does a lot of "hand-holding" for them to get them through the tricky parts. I use this activity within cooperative groups, and I circulate to make sure they are getting the purpose of the questions.