The younger your child is, the more sleep he or she will need. Usually until the age of about 9 months, babies will need about three hours of sleep in the daytime as well as sleeping most of the night. After nine months this gradually becomes less.
Some babies don't seem to want to sleep in the daytime, but it is generally agreed that they should have a little daytime nap for their health, so it is worth persisting. The most important thing is routine. If you are at home, your child will find it easier to go to sleep if he is put down for a nap in his usual bed, and if you sit down with him and give him a lullaby or a soothing chat for a few minutes as you would at night. If the child is with a minder, it's best if the children always nap in the same place every day, as routine is comforting.
It's also best if you try and put your child down for a nap quite quickly and don't wait until she is really tired as it can actually be harder to get to sleep if you are overtired (this actually applies to everyone). You can find more ideas here.