Go out into the yard and start looking around. If there's water anywhere, even a puddle or an especially wet plant, start there. Bring a friend along and have him hold the box you'll use to trap the frog and a few worms.
Get the frog away from any bushes or water where it can easily avoid you and go back into hiding. If possible, stand with your back toward the bushes or water and throw a small stick or rock in the frog's direction. The frog will jump away from the sticks and this will push it out into the open.
Tell your friend when you've spotted a frog and are starting to push it out into open space. Your friend should then begin laying down a trail of worms from your direction out into a clear, open space where he can easily trap the frog. He should then crouch down at the end of the trail while holding the box.
Run over to where your friend is standing and grab the flashlight. Shine the flashlight in the frog's face once it's out in the open and almost near the end of the worm trail. This will cause the frog to basically freeze like a deer in headlights.
Throw the box quickly over the frog while it's frozen in place. This should be done by your friend while you're still shining the flashlight at the frog.