Tips for golfing in Whitespace
I'm not entirely sure whether this is a joke question or not, so I hope I don't get mocked for taking it seriously, but...
Tip 1: Don't End Your Program
The spec says that a program should be ended by three line-feeds, [LF][LF][LF], where the first is the flow control IMP, and the next two are the quit command, but many interpreters will just run your code without the proper ending. Saves you 3 characters in any program.