Most common 'mistakes' and 'crutches' for those starting out with inform 7?

There’s an additional ‘gotcha’ here in that texts can be expanded unexpectedly by the internal workings of Inform so that Inform can examine the current result of that expansion for its own purposes. This will unexpectedly run any ‘non-outputting code’ included in your ‘To say …’ phrase. You can trap this unwanted behaviour in your ‘To say …’ code by presaging ‘non-outputting code’ by the almost-undocumented conditional ‘unless expanding text for comparison purposes …’ See here and here.