Step 1

Trim the excess off the lead lines where they connect to the bottom of the net. Put a drop of super glue on the knot and cut if off flush. this prevents the excess line from catching in the net and keeping it from opening fully.

Step 2

Fill the washing machine with hot water, add fabric softener and place the cast net in it and soak overnight. Some new nets come pre softened, but I still soak em.

Step 3

Remove the net from the softener and place in the yard, spread out to the maximum circle and steak it out with large nails. Let it stay this way all day in the sun, this helps set and stretch the net.
I personally go thru about a net a month and sometimes more, so i use the $24 net that Wall Mart sells. If a net last you a long time buy a Betts Old Salt from Bass Pro, or other hi quality cast net. The cheaper cast nets will last and hold their shape for 30-90 days just fine. After about 90 days they lose there shape and become somewaht hard to use and make open properly. This is just my way of preparing a net and find they work much easier and better if exposed to this ritual.