This will take 1-2 lessons, depending on how much time your students need writing and if you want them to share their creations at the end.
I start by introducing the class to superstitions with a powerpoint. This should be after the conditional clause has already been introduced to the students. The powerpoint gives examples of different superstitions from around the world. The students will probably be surprised at how many are similar or the same in Japan. Ask the OTE to help you check students understanding of the superstitions (student translation into Japanese). At the end encourage students to say some other superstitions. My class we allowed them to use Japanese for words or phrases they didn't know how to say in English yet, with the OTE/ALT reinforcing the If ~ then ~ clause for each one.
Sadly my powerpoint COULD NOT be uploaded (too big) but it shouldn't be too hard to make your own. Google world superstitions brings up many examples. My favorites:
In Korea, if you sleep with a fan on, you die in your sleep.
In Russia, if a bird poops on you, you become rich.
In Brazil, if your wallet touches the ground, you become poor.
**Check the sentences you'll use with your OTE before the lesson. Its easy to use future tense for these which may or may not have been introduced yet to the students - its the next chapter. Depending on the class though they may be able to figure out the meaning of simple sentences in future**
For the main activity, first I give students the worksheet where they are told to write down a number of random nouns, verbs and adjectives. Don't tell them what they will do with them and encourage them to write the most random words they can think of. Tell them their words are a secret and they can't show their friends.
When every one is finished, students switch papers with a partner. Hand out the second sheet (sentence builder) and tell them to select words from their partners word list to make sentences. They can only use each word ONCE. They should be stuck with some strange sentences that get a few giggles like "If you eat a car, you become a purple horse."
Optionally you can ask them to write the meaning of each sentence in Japanese on the back or in their notebooks to ensure they understand the meaning (even if it is super strange).