the old standard phrase: on the one hand and on the other hand...

@Helmi: IMHO "on the one hand..., on the other hand" present contradictory concepts--the hands are on opposing sides. "Zum einen..., zum anderen", in contrast, enumerate arguments for the same side.

@ oreg , it's not that unique that silly standard lines are contradictory, but that's the way it is.

@Helmi: Not sure if I was clear enough. I'm not saying that the English idiom is contradictory. What I mean is that "on the one hand / on the other hand" does not match "zum einen / zum anderen".

for one thing, it will be dark soon. for another, it looks like it's going to rain. so now is not a good time to go sailing.

first of all, it will be dark soon. secondly, it's going to rain.

alternatives:
first, it will be dark soon. second, it's going to rain. (somewhat informal)
firstly, it will be dark soon... (ok, but sounds odd to me for some reason).

...based on oreg's explanation, thanks.

also, would prefer "... Furthermore, ..."; "moreover" sounds antiquated to me.