These suggestions should be taken lightly (I don't think there's a definitive answer), but a rough guideline would be to consider the following:
- más tarde - sometime later
- después - afterwards
- luego - later
- entonces - then
- en otra ocasión - some other time
In english, if asked "Could you take the trash out?", it doesn't make much sense to just answer "afterwards". In spanish it does, but it might give the impression that you're not interested.
If used at the beginning of a sentence as a way to tie to the previous idea, they're pretty much interchangeable, except for "en otra ocasión":
Más tarde, se reunió con sus amigos.
Después fueron a comer juntos.
Luego fueron a tomar café.
Entonces decidieron ir al cine.
En otra ocasión irían a jugar billar.
Here, the first 4 statements state an action that happened after the previous statement. The fifth statement refers to another event altogether.
Translated back to English, we'd have something like:
Sometime later, he gathered with some friends.
Afterwards, they had lunch together.
Later they went to have some coffee.
Then they decided to go to the movies.
Some other time they'd go play billiards.