I created a postfield "property" for a real estate website.
I created multiple fields as number of bathrooms, number of rooms, etc... which are simple "number" values.
I created also a field with multiple checkboxes. The displayed result is in 1 line like : "value1, value2, value3"
You need to set up the markup before and after the field with the ul tags and the first opening li tag and final closing li tag, and then instead of the default comma separator use li tags like so:
If you are using Blocks rather than the legacy interface you would need to add that using a Fields and Text block in HTML mode (and you will need to edit the slug of your field, of course).