The construction stare + gerundio corresponds more or less to the English continuous form. About the main differences we have talked already. English native speakers tend to overuse this form. The main differences are:
1) In contrast to English the construction stare + gerundio is rarely used with compound tenses. Normally it is only used with the simple tenses (presente, imperfetto, futuro I, condizionale I, congiuntivo presente, congiuntivo imperfetto). In English the continuous form of the compound tenses (present perfect, past perfect) is used to describe an action which has started in the the past and is still going on in the present of the speaker.
- the action has started in the past, is finished, but the results are important for the moment of speaking. I have finished the work, know I need a coffee.
- the action has started in the past, is not finished and is still going on in the moment of speaking. I have been working the whole day on it, and it is not yet finished.
This difference is not made in general in Italian and so the continuous form of a compound tense is rarely used.
2) In English there is no special tense to describe a state in the past, to describe two parallel actions or to describe an action which has been interrupted by another action. All these functions are realized with one tense, the simple past. Therefore, the continuous form is needed. In Italian, and in all other romance languages, there is a special time for that, at least in the past, the imperfetto, and so there is no urgent need for something similar to the simple past continuous (I was reading a book...) in Italian. You can use it, but it is rarely really needed. Only if a distinction is to be made between the description of a state and an ongoing action it is needed.
- People listened to his words until he died.
meaning: People listened regularly to his words. He was a preacher and came regularly every sunday to preach. People came every sunday to listen him until he died.
- People were listening to his words until he died.
meaning: In his whole live he never talked a lot. But when he was dying, in his bed, mortally ill, the family gathered around his bed and listened to his words until he died.
If you have a situation like that, in other words if the meaning is ambiguous, you can use the construction stare + gerundio in imperfetto.
But this kind of distinctions are very rarely to be made.
3) In part the overuse of the continuous form in Italian by English native speakers, in other words of the construction stare + gerundio can be explained already by point 2). The rest is due to the fact that the continuous form in romance languages (French as well have something similar, être + en train de faire quelque chose) is only used if it is crucial for the meaning of the sentence that the action is described as something happening in a concrete moment.
To the English continuous form corresponds the construction stare + gerundio in Italian.
Stai lavorando in questo momento o puoi aiutarmi un attimo?
Are you working right now or can you help me a moment.
Giusto nel momento in cui stavo scrivendogli una lettera, mi chiamò.
At the moment when I was writing him a letter, he called me.
Lui voleva che io stessi già lavorando quando fosse arrivato.
He want me being working when he arrives.
Io starei già lavorando se lui mi lasciasse in pace.