I'm probably telling you things you already know but here are the principles:
bedtime routine:
bath, story, lulluby and bed (night light on in bedroom): be firm and consistent, keep your voice low, aviod too much eye contact when they are getting sleepy, plenty of reassurance and patience but be firm: 'it's time for bed, it's time for sleep'.
It does work, I promise, but may take some perseverence