Materials you need (and links to where I bought mine):
1. 16 inch diameter styrofoam ball. Mine came in two hollow halves which made it very convenient. http://www.plasteelcorp.com/
2. Paper. You should make everything out of paper before using the real stuff.
3. Serrated knife. I used a kitchen steak knife type thing.
4. Glue. I used a hot glue gun. Other glue might be ok.
5. Scotch tape and masking tape or other "wide" tape.
6. Pens, markers, pencils. Helps you draw your shapes before cutting.
2. Cut out a hole to fit your head in. You'll want to have the head's face on one of the half sphere's, not along the seam. Cut accordingly. My opening was about 8.5 inches in diameter.
3. Cut circles out of paper that are the size you want the eyes. My eyes are 3.5 inches in diameter. Cut some more paper in the shape of the mouth. Color these, then tape them to your head. Make whatever adjustments here.
4. Remove the eye circles, and cut out holes in their place. You want your hole to be smaller than the full size of the eye, so that the eye can be glued on the head. For example, if your eye is 3.5 inches in diameter, make the hole around 2.5 inches in diameter.
5. Cut your mesh into circles that will fit over the eye holes. These should also be less than total the size of the eye, but more than the hole. Try 3 inches diameter.
6. Glue the mesh over the eye holes.
7. Cut the full eye-sized circles out of blue craft foam. For the inner circle that you will cut out, I used a razor blade. Exacto knife, something like that will work. Using scissors for the inside will probably not cut cleanly.
8. Glue the eyes over the mesh.
9. Cut the mouth out of red craft foam, put it on head. I found a sticky-backed craft foam in red, so after cutting it, I was able to just easily stick it on the head. No glue required. It also seems like it can be easily removed to be replaced with other mouth shapes. Go wild.
10. For the nose, I made a cone out of black craft foam. I found a great tutorial on making cones here: http://www.firstpalette.com/tool_box/quick_how_to/Cone_Hat/Cone_Hat.html . Basically, cut something between a half circle and quarter circle, then form the cone. Do this with paper first to get a feel for it. I went with something like a 3/8th circle.
11. Form the cone for the nose. Tape this together with a few pieces of tape. Then remove the tape one by one, gluing the thing together. After it is dry, glue nose to head.
12. For the inside, I lined blocks of padding foam in the back, top, and two sides. I taped them all with masking tape.
You're done! If you want to make a hat, you can do this by making a big yellow cone, then a long rectangular base thing for the bottom of the hat. Look at some pictures, you'll figure it out.