Join your local Toastmasters group. Search for entrepreneur focused dev meetups (we had an “unconference” in my area where you could give a speech on any topic) or the age old friends and family party now please listen to and critique my 20 minute pitch.

Attend pitch competitions. Don't take them seriously, just get the reps in and you'll be ready when it counts.

Also, share your idea whenever you can with whoever you can. You'll generate signal over time.