It's important to use a wool or wool blend felt for this project, you want the leaves to be nice and thick and hold their shape. You'll need three sheets of 12x18 inch green felt, and one 9x12 (or less) of white and yellow.
First cut two 12x12 inch squares from your large sheets of felt. Then cut out 30 leaf shapes. I've made you a handy pattern for the leaves and flower.
Cut a slit in one end of each leaf (about 1 1/2 inches) and over lap them like this. This will help the leaves stand up give them a little more dimension.
Find the center of one square and start stitching the leaves in place around it. Overlap them a bit on one side.
I'm using this very basic applique stitch to sew them on.
The first leaf layer will be a circle made from 6 leaves.
Next, stitch 6 more leaves in place behind the first layer. Keep adding leaves around the circle until you fill up the whole square.
Now cut out the flower and center shapes from the pattern and stitch them on in the middle.
When everything is sewn in place, fold and pin down the outer leaves like this (so they don't get caught in the seam), then pin the back square over top. Sew around the outer edge, leaving 3 inches open on one side. Snip the corners off flat, turn your pillow right side out, stuff and stitch up the opening.
Here is a good way to sew up pillows or stuffed animals, that will leave your open space nearly hidden.
Start your knot on the inside, stitch straight across the gap, then up along the side on the inside, across again, and so on down the seam. Tie a small knot right in the seam and it will be barely noticeable.