Blood will Flow

If you have a DW account, you go to the home page and the Organize tab. The drop down list gives you an option to import and when you click on that you just follow the steps it gives you. You can import from LJ or Insanejournal. You have to give the login details then tick the boxes of all the items you want to import. I usually just tick all of them.

Oh and when it starts, it's worth refreshing the page after a minute or so to make sure the login has worked (if you're like me and liable to mistype stuff). Other than that, you just leave it running.