These are really simple. Most fabric stores have mounds of bolts of this type of material. Although maybe not so much right now as in November!
Anyway, figure out how big you want the finished blanket - ie: crib, afghan, or twin bed. Most of these are about 54" wide so the width is set - the selvage edges eliminate the need to sew the sides so don't make them narrower. Add to the length you want the length of the fringe plus a little bit for the knot.
So for instance if you wanted a throw for a 6 foot tall teenage boy that plays football do the following.
1. Go to the fabric store and select a fabric.
2. This is a tall person so I'd make it about 2 yards of finished, solid fabric. Plus fringing so let's call it 2.5 yards.
3. Take it home and wash the fabric.
4. Lay it out on a surface so that the end you're fringing is laying flat.
5. Cut into the fabric with good sharp shears about 8".
6. Tie a knot tight to the fabric where the fringe cut stops.
7. Switch it around to the other end and repeat steps 4-6
Viola'! Finished blanket. The length adjusts, and the fringe length is a matter of personal preference. Another way to do this is select the length you want plus about 2" and then do a turned hem on each end that you sew with a regular machine stitch or you can do the blanket stitch.
Most fabric stores have flyers available that show that stitch in a step by step illustrated manner.
Have fun!
Deb