Do not neglect their playtime during the day. You should help to ensure that they get a healthy level of play during the day so that they can sleep better once night comes around. In addition, set certain rules regarding bedtimes and expect them to stick to it. Finally, if you can do so, start by setting the example as best as possible.
You will find, especially with the last one, that once parents are asleep most children will also have no trouble getting into bed. You can help the most by emulating the right kind of behavior that is expected.