It is always a struggle to put the kids to sleep. But not always if some essential things are taken care of.
Fill their tummy:
A kid cannot sleep if he/she is hungry or half-filled. Make sure to give some kind of solid food/milk before their sleep time.
Check the diaper:
Check and change the diaper before sleep time to make them comfortable and get relaxed sleep.
Do not push them:
It is not easily possible to fix a time for their sleep. Change the environment to sleep mode by switching off the TV, lights, and obviously mobile phones.
Some kids need pampering like they want to sleep on mom/dad, or they want to lie with them to get warmth and comfort.
Make them tired:
Yes! Play with them and keep them engaged. This will increase their desire to eat and sleep soon.
Most of the kids wake up once or twice during their sleep. It is necessary to know their wake up time and give milk/solids to get them to sleep again. Try not to make them fully awake and cry. Some kids wake up just for water.
Some kids might eventually develop a habit of thumb sucking when they are in need of soothing or going to sleep. Make sure to release their thumb after their sleep.
*All the above mentioned points are from personal experience!