"Then" and "next" both make the narrative sound more like a list: This happened, then this happened, then this happened...

Readers will assume that the flow of causality is the same as the order of sentences, so if you were to write "Michael started screaming. "Why are you screaming?" Lily asked. The kid named Crystal began to dance," the would know that Michael screamed, then Lily spoke, then Crystal started dancing. You don't have to add "then" or "next" at all.

For another example, what's more interesting?

This:

Absently, Alcina set a candle out and lit it.

Purple light flared, impossibly bright. Alcina shrieked and ducked instinctively.

Something went sSSKRWEEE.

A good while later, Alcina peaked over her forearms. The countertop and the wall behind it had burned to cinders. Little dollops of purple fire still flickered in the pile of ash that had been the candle. Beady droplets of melted blue-white-and-yellow countertop tiles oozed slow tracks down the wooden cabinets below, leaving charred grooves in their wake.

And Alcina thought, Aah.

A while later she woke up again and finished her earlier thought with, oh, that’s not good. When she collected herself a little bit more and managed a good look at herself only to realize that every single piece of protective jewelry that she wore had melted slightly, she revised to, Ah, Tíw. 

Or this:

Then Alcina set a candle out and lit it.

Then purple light flared, impossibly bright. Then Alcina shrieked and ducked instinctively.

Next, something went sSSKRWEEE.

Then, Alcina peaked over her forearms. The countertop and the wall behind it had burned to cinders. Little dollops of purple fire still flickered in the pile of ash that had been the candle. Beady droplets of melted blue-white-and-yellow countertop tiles oozed slow tracks down the wooden cabinets below, leaving charred grooves in their wake.

Then Alcina thought, Aah.

A while later she woke up again and finished her earlier thought with, oh, that’s not good. Then she collected herself a little bit more and managed a good look at herself only to realize that every single piece of protective jewelry that she wore had melted slightly. Then she revised to, Ah, Tíw. 

The point is that you don't need to use "then" at all, or sparingly if you do use it. Practice writing passages without using "then" or "next" at all. It'll be hard at first, but it'll get easier the more you practice, and your writing will be more interesting for it. 

My teacher in fourth grade taught us to use these different transition words.  This applied to essays in her class, but it could also be used in fiction.  (For future reference, you could get much help on the Writers' Help Thread.  More people might look at it.)