A starter can be used as a useful ‘revision bite’ to keep topics in mind that might not have been studied for some time.
Try the brilliant collection from Corbettmaths: 5-a-day.
GCSE Higher Revision Starters from a mathematics teacher in Berkshire who has adapted an Edexcel resource.
Questions from the tests from the BBC GCSE Bitesize site can provide a starter to revise the topic of your choice.
Try a Mini-test; help students with their recall.
For more on revision activities see this collection.