Avoid assigning the topic to students currently assigned on other tasks (e.g. writing, revising)
Double-check that the referee is not a co-author!!
On average, twice as many peer-reviewers as there are authors
Furthermore, assign the guest lecturer as author
In total, students should do 2 peer-reviews over the course of the semester, so keep in mind future constraints when assigning students (e.g. students writing a review on the 2nd last topic need to finish their two peer-review assignments by then!)