This means keeping many trails open at once, inevitably requiring a fairly 'parallel' plot. This plot should be discovered rather than announced, so show, don't tell.

If you're setting a game during the Cuban Missile Crisis, look through a library. find out what people were wearing, what other issues were in the news, how houses were furnished, what cars were being driven. Especially include things which now seem foreign.

Writing a really general parser is a major but different undertaking, by far the hardest points being sensitivity to context and resolution of ambiguity.

I try to make puzzles range all the way from easy to hard, and to leave many open at once.

The 'interactive fiction' format hasn't changed in any fundamental way since the early 1970s, in the same way that the format of the novel hasn't since 1700.

What I would pay much more attention to are the few points where the player can inadvertently make a career decision. Most players end up back-tracking, though some actually enjoy this.

This means keeping many trails open at once, inevitably requiring a fairly 'parallel' plot. This plot should be discovered rather than announced, so show, don't tell.