I was in the same exact position as you just this morning! I spent about an hour reading over threads about this topic (there are SO many different suggestions... ugggg) So I threw up my hands and spoke with a local livestock owner at the feed store.
Here's the route I took earlier today.
Step One: Purchased a bottle of livestock permethrin dusting powder, and food-grade diatomaceous earth.
Step Two: Drove home
Step Three: Put on some protective gloves (and bandana to cover my mouth/nose)
Step Four: Gently hold the chicken in one arm and take a little handful of powder in the other and "fluff" it underneigh the wings, neck feathers, vents and belly
Step Five: If needed, apply more
Step Six: Rake out all the bedding from house/run.
Step Seven: Apply Diatomaceous Earth (DE) to all corners, flooring, nesting area and put new clean bedding in the house.
Step Eight: Dust with an old kitchen 'sifter' the run with DE. The chickens will take dust baths and roll in it (FYI- DE works as a preventative, it doesn't kill Lice as far as I know...)
Step Nine: If there are little eggs (white clusters at base of feathers) you may need to reapply Perethrin Dust in 10 days once eggs hatch (Dust doesn't work on eggs, just hatched lice).
Step Ten: Strip clothing, put in washing machine and take a shower
Phew... I think that is it.