I find mealworms easy to raise. They are in a covered box with screened lid (very fine so they don't escape). The substrate is layers of paper towels and bran. They eat the bran, and I sprinkle the top with water 3 times a week. I give them slices of apple, pear, carrot, etc. for moisture and extra food. They will eat any grain though. They even chew through hamster block food, so don't worry about grinding anything fine. When the bran gets powdery, I add more on top.
Don't throw away all the substrate when you clean, it will contain the eggs of the next generation. I mainly pick out the dried up/bad fruit bits. Maybe twice a year I do a thorough clean out and start over the substrate, but try to keep all stages of mealworms and beetles so you don't get stuck with a dry spell.
I use a kitchen sifter to sort the mealworms from the beetles and substrate when feeding. I feed all sizes of mealworms, they chickens don't care how big they are.
Be careful they don't escape into your house or they will find the kitchen and eat all your cereal, etc.
