Again, try the clock. When Nick gets in bed at night now, he says, "I wait a seven-zero-zero." Since he doesn't go to bed until around 7:30, it's a long time to wait for that to come around and he falls asleep.
Make a big POSITIVE deal out of staying in bed, not yelling. I know. It's hard. I've yelled. I'll probably yell again. But the yelling will associate negative feelings with bedtime and staying in bed and then he really won't want to do it. Nick moved into his bed at about 20 months and for the second and third month of that transition, we just had to take him back to bed, without words, time and time again. He eventually just started staying there. The whole without words helped keep us calm which in turn kept him calm.
And honestly? Leave some toys in his bed that are just for bed. Explain that he can't take them out of bed. At this point, who cares if he plays for a little bit as long as he stays in bed? Nick now no longer does this but for a long time, we had to make sure all of his cars were in bed with him.
Our current battle with our two and a half year old is that he KNOWS if he says he has to pee or poop, we'll let him out of bed. Oh, manipulation starts early!