Wind your thread to the bend of the hook as shown so that the fibre ends up to one side.
Cut a piece of 2-4mm foam as shown, and tie it on.
Move your thread towards the eye of the hook.
Fold the foam over (just like a flipper) and secure as shown.
Do a safety knot.
Trim the front of the foam, so its just about in line with the end of the eye, and cut off any excess so you have a taper.
Cut a piece of felt about twice the length of the hook, and wide enough to almost wrap around the foam in the centre.
Make two little folds in the felt to form a tail before tying on and securing with a half hitch.
Turn the fly over, and tie back the fur that was sticking out.
At this stage it is a good idea to do half hitch after every step.
Now you can start tying the segments. You can move the thread from segment to segment, but also tie each one off before starting the next one.
This is much neater, but slower, and I doubt the fish will notice the difference. As you move from one segment to the next, pull back some of the fur before you go to form the legs as shown.
Finish off the thread, as you won't be needing it any more.
Once your segments are done, turn the fly over, grab a bunch of fur and by rubbing a scissor blade up and down, you can trim them.
Using this method gives a tapered natural effect.
Turn the fly over again, and at this stage you may want to put a drop of head cement on each thread at the top.
Not a lot, just enough to bond the threads together.
Slit the felt down the middle, and then trim the right side short as shown.
Then you can use your artistic abilities to shape the claw.
With a wire brush, fluff up the felt a bit as it makes the fly look more realistic underwater and breaks up any sharp edges.
That's it, no fancy legs or shrimp eyes required. Use colours that match the prawns where you will be fishing. If fishing over a mud bank, you can rub your prawn in the mud to get it to match the mud pawns.
If you want a floating prawn, use a bit more foam, and a lighter gauge hook.
Fish with as long a leader as you can handle, and a tippet piece of fluorocarbon will certainly help.
You want the fly to land gently and without plop which will scare off the fish.
If you want it weighted, use bead chain eyes at the bend of the hook, build up the body shape with strips of felt, and do the body upside down so that it swims hook up.