It honestly depends on the cause of your insomnia. If it is a chronic issue I would suggest speaking with a physician or doing a sleep study. While herbs are a wonderful means of natural medicine, they can still cause issues like side effects and or interactions with other medicine.
Many things cause sleep issues. From what I have read one of the most common is not getting enough exercise. However, exercising too close to bedtime can actually make sleep more difficult.
A few herbs/supplements that are fairly safe for sleep would be chammomile (as others suggested), valerian root, melatonin (hormone), and lavender.
Aromatherapy helps some individuals. You can use scented candles, sachets, baths with scented epsom salts or oils, incense etc.
Limiting your use of electronics and being active in your bedroom is also said to help. Psychologist suggest turning off tv, computers and the like one hour before bedtime.
Meditation and relaxation are a big help for many. For further reading on relaxation I suggest this post
this technique was taught to me many years ago and helps tremendously when trying to sleep or prepare for entering other realms.
Love, light and blessings