I am a trifle rusty at this, but:
Quick and Dirty Cum Clauses
Causal (cum=since) and Concessive (cum=although) clauses take the subjunctive, tense determined by the main verb.
Temporal (cum=when) clauses referring to the present or future take the indicative (pres, fut or fut pf) (fut for incompleted action, fut pf for completed)
Temporal clauses referring to the past take the subjunctive, impf to show incompleted action (translate cum as when or while); plupf to show completed action (translate cum as when or after).
Present temporal: times happen when things go badly
Future temporal incompleted: I will not hesitate to call on you when it is convenient
Future temporal completed: You will find out when you get here
Past temporal incompleted: I received your letter while/when I was resting
Past temporal completed: He left after/when he had finished speaking
A few further frills:
Temporal clauses occasionally use past tenses of the indicative to date or define the time of the action of the main verb--in this context cum is generally found in the combinations tum cum (at the time when) and eo tempore cum (ditto). The subjunctive may also be used, however.
Finally, when the expressed subject of the subordinate verb refers to the same person as that of the main verb, place the subject first, followed by the cum clause.
I hesitate to cite examples because on the one hand made Latin is highly unlike the real thing and on the other, I don't like to snow you with a bunch of unfamiliar vocabulary and forms by quoting.
In terms of your example from Wheelock, I myself would be strongly inclined to put the cum clause into the pluperfect--I closed the door after I had entered the house.: Cum domum introissem, januam clausi. Which I know doesn't really help you at all, I'm sorry
I hope this helps!