I just taught will for predictions this weekend. It's quite easy once you have a few ideas. A couple of things I did, if you're interested:
Class survey
This was from Cutting Edge Pre Int resource book (I think). So they are each given a piece of paper with a category on it (home, travel, work, etc) and hints towards 7 developments they might expect to happen by 2020 (written in note form - e.g. "people...live on moon"). They then have to write the question for each one, and then conduct a survey with all of the other members of the class (a simple template for them to write their survey on will help). For feedback, they can then report their results to the rest of the class. "7 people think that people will live on the moon by 2020." You can also get a bit of intonation in here, after they've written the questions but before they've asked it. Simply write a couple on the board and ask them if they go up or down at the end of the sentence.
Circle Mingle
I don't know if this has an official name. Prepare some questions with will on little cards. They have to be general questions that anyone can answer (e.g. Which country will win the most medals at the 2012 Olympics? Will Barack Obama still be president in 2015? Will you marry me?). Get the students to stand in a circle, and you stand in the middle. Ask a strong student one of the questions on the card. When they've answered it, give it to that student and indicate for them to ask the next person. Keep doing that until all of the students have cards and they're all asking their question and swapping cards. You shouldn't need any verbal instructions at all for this activity, which is good for CELTA (if you can draw a circle on the floor before they stand up, that would be useful, but that might just be my school that lets you do that). It can keep going until everyone has asked and answered every question. Be prepared for students who horde cards.
Pronunciation of contracted forms
"I eat dinner" or "I'll eat dinner."
I did a few from the CD, where they have to listen and identify which was said, and then I wrote ten out and did them as a running dictation (although at this level, they have a habit of reading "I'll" as "I will" so make sure you drill it with them first and don't let them say "I will").
Presentation
This one might take a bit long for a 40 minute class. In groups, they draw a new invention and write some sentences about it using will. They then have to deliver a presentation to the class. The best way to structure it is for you to do exactly what you expect of them at the start of the lesson. You'll also need to give them a bit of presentation language. As an extra task, you could also prepare some questions that the students have the answer about each presentation (i.e. What is the name of the invention? How much does it cost?) to force them to listen to their classmates.