How to get an early toddler to sleep?

My baby boy is almost 18 months old. He has naps during the day, eats every meal, drinks his milk, and we try to sleep him at the same time every night. However, he fights to stay awake and also wakes up One or two times at night. We have tried the Nanit tips, nothing works. What else could we do so all of us sleep through the night?