This thread is the best information I've seen on worming.
Threehorses Worm Thread
https://www.backyardchickens.com/forum/viewtopic.php?id=213065&p=1
What you are looking for is not just lice but also mites. I'll give you another site to cut down on my typing. It also has pictures, which helps. Lice are not a big danger to chickens but do make them uncomfortable and can reduce their productivity. Mites can kill chickens. Mites especially can live off the chickens for quite a while so you need to treat the coop as well as the birds.
Ohio State Mites and Lice
http://ohioline.osu.edu/vme-fact/0018.html
I don't treat for lice and miites unless I know they are present. I don't think treating twice a year will do any damage or harm as long as you also treat if you see them. There are different treatments for different mites and you can either dust or spray so my answer will not be real complete.
Sevin is a popular dust to use. There are others that are effective. You can put Sevin in a nylon stocking and dust the bird with it like it is a powder puff. Especially get the vent area but you need to get the whole bird. Or you can put the powder in a garbage bag, put the chicken in the bag to the neck, hold it closed around the neck and agitate. Do it outside where there is good ventilation. It is recommended to wear a face mask and try not to breath too much of the dust. Try to reduce how much the chicken breathes in too. Or you can use a spray. Again, spray the whole chicken except the face, wear a mask, do it in a ventilated area, and minimize what the chicken breathes.
If you have an infestation of mites, you need to change out the nesting material and the bedding and treat the coop. Dust or spray the nesting boxes and the roosts especially. If it is the red roost mite, especially get every nook and cranny you can find. They live in these during the day and suck the bird's blood by night.
This treatment does not get the eggs. They have a 10 to 14 day life cycle, so you need to do it again in about two weeks. I would not change out the litter but I would the nesting material for the second treatment.
Sevin and most sprays for mites and lice do not effect the eggs. Most worming products do. You'll need to check the specific product you use.