Soak the backyard with a garden hose at dusk. Watering in the evening hours reduces evaporation and helps the soil absorb moisture, which drives worms faster to the surface.
Drive a shovel blade into the edge of your backyard where the soil is wet. You can dig anywhere you like if you don't mind shovel holes all over the yard, but digging at the edge will be less obtrusive.
Shine a flashlight onto the dirt mound overturned with your shovel. Poke at the dirt to loosen and expose worms.
Grab a worm gently with your thumb and index finger when you find one wriggling in the soil. Hold the worm for a moment rather than pulling immediately to avoid pulling the worm apart. When the worm stops resisting, pull from the soil and deposit in your bucket.
Overturn shovelfuls of dirt to catch worms until you've found as many as you need. For a fishing trip, plan on using a dozen worms for bait per person.
Cover the worms with a layer of loose soil and sprinkle lightly with water. Add a few pinches of crackermeal and keep the bucket in a cool, dark place until needed.