There are 2 main ways to tie a Karate belt. There’s a traditional way and a more modern way. The actual knot is the same in both cases, but the way that the belt is wrapped around the body is slightly different. Looking on Youtube, I note that Judo and Ju Jutsu practitioners tie their belts the same as Karate’s traditional way; so this would appear to be a general Japanese way of doing things.
I’m guessing, but I think the more modern way has come across from Tae Kwon Do as you can also see on Youtube that they do it this way. It is actually a little bit neater, but the choice is yours and it doesn’t really matter.
So here it is in the video below. Enjoy: