Step 1: Have several hens from breeds that are known to go broody a lot.
Step 2: Wait and hope you are lucky.
I don't know of anything that actually works to make a hen go broody. It is a hormonal thing. When the hen's hormones tell her to go broody, she will. I have had several hens that seem to want to go broody but never follow through on it. They spend time on the nest and fluff up and cluck when they are walking around, but don't spend the night on the nest. That proves to me they are not serious. I had an Australorp that did this but also spent one night on the nest. The next night she was back on the roost, so I locked her in the nest for that night, all the next day, and the following night, with food and water available. She spent 3 weeks sitting on fake eggs and raised 15 incubator-hatched chicks for me. If a hen's hormones are acting up, locking her in the nest may be a way to help get her over the hump. I think it may have made the difference in mine. But I think the hormones have to be acting up to start with for it to have a chance of helping. I've seen the write-up Ddawn is talking about. That's what made me think of locking a hen up that was tending that way to see if it would help. But locking a hen up in a pitch black nest for a few days with no food or water just seemed too cruel for me to try. When I did what I did, she had a fairly dark nest but an area to the side with food and water and enough light she could see to eat and drink.
Some people believe that letting the eggs pile up in the nest will make a hen go broody. Adding one egg a day has not worked for me. If you read the posts on here, you will see a lot of hens that go broody on just their imagination. They don't need actual eggs. It may help if a hen is feeling that way to start with, but I can guarantee you that letting the eggs pile up is no guarantee a hen will go broody, even from breeds that often go broody.