When displaying delta percentages, I like to show them slightly different than hitting the standard % button.
Depending on the value, the – sign is not as visible, and I usually want to show a + sign before the positives as well:

This is accomplished by setting the cell format to custom and then :
_(* "+"???0%_);_(* "-"???0%_);"-"
When you want to display values instead of %’s, I prefer the following:
+* #,##0_-;-* #,##0_-;_-* "-"??_-;_-@_-
This is essentially the ACCOUNTING format, but it shows positive values with a plus (+) sign!