Students of English often fall in love with specific tenses. English teachers are somewhat guilty in that they overemphasize certain forms of the verb because they are either easy to teach or demonstrate. The classic example is the present progressive, am/are/is ___ing, but the past progressive is also generally over and misused by Israelis.
To clarify the matter, the past progressive, was/were ____ing, has three specific meanings:
a. The most common – an unfinished action that must be completed by a verb in the past tense: I was walking home when I saw an elephant. I was on my way home, but did not reach it. You cannot have just the past progressive. It is like throwing one shoe and leaving the listener/reader waiting for the other shoe.
b. Two or more simultaneous actions, all in the past progressive: you were sleeping while I was cleaning the house.
c. Rare: asking about a specific action at a specific time in the past, as the police or your parents would do: What were you doing at four o’clock in the morning in the park? (Parents really don’t want to know!)
In terms of other languages, the French imparfait is not really the equivalent. It emphasizes repeated actions, such as Je dormais toute la journée quand j’avais 15 ans (I used to sleep all day when I was 15 years old). The closest in terms of the first meaning is j’étais en train de rentrer chez moi quand je suis tombé. Russian has the imperfect aspect in the past tense (несовершенный вид). One of the uses is for unfinished actions as in я открывал окно [ya otkrival okno], I was opening the window, which implies that the window has not been opened.
As a rule, do NOT use the past progressive unless you want to say that the action was not completed. The other two uses are in fact very rare.