Use a piece of card board cut the same size a a sheet of paper 8x11. You can simply lay a piece of paper over your cardboard and trace around. Cut. If you don't have a handy-dandy paper cutter like this just use a ruler to mark line and cut with scissors.
Thread your cover design by hand using the holes you made in the journal cover. For further instructions on how to do this you can visit Little Monster, where I offer a more in depth tutorial on the embroidery process.
After you have finished the embroidery work sew the paper pages together on your sewing machine. You might want to test this process first. Adjust tension to loose setting and set long stitches. Then place your paper inside your cover and sew again. Tip: use a new needle and be sure this needle will no longer be of use for fabric projects.
Once your journal is all done you can decorate the outer seam with washi tape and wrap it up pretty with some extra embroidery thread.