Another way to do it would be to actually draw a world map from memory. Unless you're some kind of eidetic wizard, you'll make mistakes, leave things out or add 'em, get dimensions wrong, etc. Then you can go in and alter things; make that Yucatan peninsula even bigger; chop off Florida; add a few dozen more islands to Japan, etc etc. It'll still look recognizably like Earth, but a base map drawn from memory and then fiddled with like that would probably be sufficiently different.