The most important thing for better sleep for your toddler / preschooler is ROUTINE.
Bed time should be a good experience for the whole family. It could be the highlight of the day. A snuggly time for love and kisses. So how do we make this happen? It is not as hard as you think, and you can do it without letting you child know. About 45 minutes to an hour before bedtime dim or turn off some lights to make it a little darker. Our bodies naturally produce melatonin as the natural and artificial light begins to wane. Melatonin helps make us rest better. Change activities from busy to mellow. Put on soothing music (only for bedtime). Evening bath time should be warmer and more soothing than morning fun time baths. If you think you’re child will be soothed by a warm bath, try it! Brush teeth, wash face, etc. with gentleness and soothing words. 
Dress children warmly, have him/her pick out PJ’s, a sleep toy/blanket and 1 or 2 books to read. You can even do this at dinner so they have something to look forward to! Do not do more than 2 books. There should be no negotiating at bedtime. Read books and Snuggle. Once it is time to actually sleep your child should be encouraged to dream amazing dreams. You can even have them tell you what he/she will dream about. Then, lights off… night lights on dimmest setting. You may leave books for them to continue reading. Smiles, kisses and hugs. Then leave your child to sleep. He/she needs to learn to do this independent of a grown up.
TIPS: Give yourself a longer wind down time until your routine is well established. Remember to dim lights. Make bedtime the same each night. Preplan books and PJs. Make sure your child is warm enough to sleep. Return your child to his/her room after a setback. Encourage your child to learn to sleep in his/her bed. Be aware that patterns become habit. Make sure you are helping your child create good sleeping habits.