A lot depends on the size of the net. There are different methods of throwing different size nets. Remember that no centrifigal fource is required to get the net to open. Ever. It is only required to get the net away from you. If yours came with instructions that may be the way to go unless they say throw it like a Frisbee or you can find something more comfortable. For nets 8+ feet in diameter I use the "Dirty Mouth" method as described above and have acquired a taste for certain bodies of water over the years. If you are throwing a banana (I believe that is the proper term) you are most likely letting go of the lead line closest to you too soon. The other thing is you don't want to go for the distance record that will come in time. You will find that you can even do a kind of slow motion cast so that you can see how the net is leaving your hands but it should still open up. From there you just speed things up to get more distance. All you have to do then is find the bait fish. Soda crackers or crumbled up stale bread works for bream (and spottails if the mesh is 3/16 to 1/4) but they get smart fast or a crappie light or dock light that has been left on for several hours is your best bet for shad and bluebacks.
hold on with your lead hand a little longer and put a little spin on it by following through and bring your hand back to your body. It will cause it to open up more.
I feel you pain. I could not throw a net for the longest, then I found the awesome wonder that is utube. After a few visual lessons I was throwing and the net was opening all the way and I was finally catching bait. No more buying worms, shrimp, or gizzards for me.
every thing is on you tube I learned how to clean catfish, how to build crawdad traps all kind of cool stuff. I need to check out the cast nest vids.