If they return just go back to focusing on the breath again. You will get better at it with practice. Alongside this it's useful to join a meditation group or to try it alone. This got me into the habit of being still even when my thoughts were racing. Gradually my mind slowed down to match my body.
Modern life is full of people running around like headless chickens.
Although we may lead busy lives, an ability to meditate can be used in a few snatched minutes even in the busiest day if we are looking after ourselves. As well as helping ourselves mentally we can also use physical intervention. I tried using herbal preparations for insomnia for a while but although they were of some help, I was becoming increasingly sleepy throughout the day. If, however, you are drawn to herbal medicine you might like to make infusions of valerian or passionflower to drink at bedtime. I finally decided to explore the homoeopathic option and found that there were remedies to suit different types of insomnia.