Start the night right.  Children who go to sleep alone at night are more likely to go back to sleep on their own when they wake at night and find themselves alone.  If you've been helping your child fall asleep by staying with her, you've also been helping to perpetuate her night-waking habit.

Consider her comfort.  Being physically uncomfortable makes it difficult to fall back to sleep.  Try to keep the temperature in your toddler's room neither too hot nor too cold.  Wiggly toddlers tend not to stay under the covers long, so try dressing him in heavy, footed pajamas during the chilly months.  Switch to lighter nightwear and coverings in the spring and fall.  During the summer, a diaper may be sufficient on the hottest nights unless your child's room is air-conditioned.  Try to discover whether your child sleeps better in a dark room or one lit with a night-light, and then adjust the lighting accordingly.  If noise disturbs your child, close the bedroom door.  If she sleeps better when she hears you moving about, leave the door open.

Wait out whimpering.  Many parents make the mistake of responding to the slightest whimper, and end up fully waking a child who was only half awake and might otherwise have settled down by herself.  Toddlers are noisy sleepers, and it's important to recognize that most of the noises they make during the night don't require a response.

Check out the situation.  If whimpering develops into crying, slip into your child's room to be sure she isn't sick or tangled up in the covers.  Straighten out her bedding, if needed.  Change her diaper if it's dirty or wet, preferable without taking her out of the crib and with only a dim night-light on.  If she's standing up, lay her down and tuck her in again.

Offer quiet comfort.  Keep the reassurance low-key.  The idea is to help your child comfort herself, not to do the job for her.  Without talking or picking her up, gently pat or stroke her back for a moment.  Add a soothing, "Shhhhh....." if necessary.  Wait until she's calm, but not until she's asleep, and then quietly tell her that you're going back to bed now and leave the room.  If she begins crying again, wait five minutes before going back in, and then repeat the comforting process.  If the crying resumes, continue this process, each time adding five-minute increments until you're waiting 20 minutes between visits to her room.  At some point, she will go to sleep on her own.  Over the next couple of nights, the number of crying periods should drop, and by the fourth or fifth night the crying will probably stop entirely.
Mixing Days & Nights
Mixing Days & Nights
Other topics
Babies tend to get their days and nights mixed up.  Some end up sleeping more during the day than at night.
How to reverse mixed days and nights
Treat daytime naps differently from nightly bedtime routines.  During the day, let your baby take his naps anywhere in the house, but at night, put him in his own room.

Don't let your baby sleep more than four uninterrupted hours during the day.

Stimulate the baby more when he's awake during the day by singing or massaging him.  But at night, be quiet and businesslike during feeding, and keep the room dark.
Sleeping through the night
When your baby starts to sleep through the night during his first year is one of the issues new parents are often concerned about.  As a new parent, you'll probably hear about babies who have slept through the night since they were three weeks old, and you'll wonder why your child is still getting up twice a night at 10 months.  Not much can be gained by these kinds of comparisons except frustrations, so don't let it worry you too much.

Very few babies will really sleep through the night without waking up during their first year of life.  In a recent study of night-waking in infants, less than 20% of a group of 9-month-old slept without waking at least once between midnight and 5 A.M.  Another survey suggested that breast-fed babies are more likely to wake up during the night than bottle-fed babies.

Night waking is normal.  What is not normal is not being able to get yourself back to sleep.  During the second half of the first year, babies should start learning to go back to sleep themselves.  If she is always tended to when she wakes during the night, she won't learn to fall back to sleep on her own.  Whenever she awakens, she'll stay awake until you provide her with the comfort she's come to expect, whether that comfort is in the form of a bottle, a pacifier, cuddles, or a place beside you in bed.