How to create 'preferred choice' or 'ranking' in form

Have created a form but stuck on one part where there are a number of choices to a question and the user needs to be able to show their preferred choice. There will be 8 choices in total and the user will need to select their first and second choice, a simple 1 and 2 will suffice, but I don't want users to be able to repeat values. Previously a ranking wasn't required and the form used checkboxes, but it now needs to be more specific, is there a script that can be applied here?