First gather things together.
Cut a piece of card to approx 17cm x 3.5cm (made to fit the average softback book).
Either print out a head design from the internet or draw a design.
I just scribbled one here!
Make the design no wider than the width of the card and probably about the same high. So in this case the head is about 3.5cm x 3.5cm.

Cut out head design and arrange on felt as I have done above the card, leaving about 3mm on the right hand side.

Draw around head.
Draw around card leaving about 3mm on all sides but draw a tail on opposite end to head.

(Click on pic to enlarge to see what I mean)

Flip the card over (leaving another 3mm from the dashed line).
Draw around card but include legs either end.

Cut out felt! (but not down dotted line!)

Put double sided tape (or glue) on card.
Put in the centre of one side and fold felt over to cover (making sure there is still the 3mm gap).

It should resemble this!

Get a needle and thread and blanket stitch around the edge (what the extra 3mm border was allowing for!)
and running stitch when you get to the legs/head/tail.

The sewing is half for decoration half to sew up the open side.

Decorate!
Glue on bits of other coloured felt, or paint or draw on!

Put in book!

Other ones I have done are a black dog and a pangolin (with him curled at the bottom and his tail wrapping around the top of the book - see other pics!)