Formal:
* Subsequently
* Following that
* Henceforth
* From that time forward
* After that time
Informal:
* After
* Later
* Then
* From then on
The best word to use will depend on the context and the tone of your writing.
Formal:
* Subsequently
* Following that
* Henceforth
* From that time forward
* After that time
Informal:
* After
* Later
* Then
* From then on
The best word to use will depend on the context and the tone of your writing.