There is one thing you should never do, never, never, never. The Italian gerundio corresponds to the present participle in English and NOT to the gerund. The Italian gerundio CAN'T be used the same way you use the English gerund and the English gerund CAN'T be translated with a gerundio. The gerundio corresponds to the present participle in English and the English gerund is normally translated with an Italian infinitivo.
We have already said that the gerundio in an infinite form, doesn't reveal by himself who is its subject. In English you can deduce who is the author of the action described present participle from the position of the present participle in the sentence.
The present participle has the same subject as the finite verb
Laughing they saw her. The subject of the present participle is the direct object of the finite verb
They saw her laughing.
In English it is very well possible and normal that the present participle has his own subject. For details see http://www.inglese-online.de.
In Italian normally the subject of the gerundio is the subject of the finite verb. In Spanish the gerundio can have his own subject, but this kind of construction is controversially discussed in Italian. In Spanish the direct object can be the subject of the gerundio.
Las cebollas pierden su valor sumergiendolas en agua caliente.
The oignons loose their flavor if they are dipped in water.
Le vi haciendo sus maletas.
I saw her packing her bags.
(example taken from Vera Morales, Spanische Grammatik, third edition, page 296)
In Italian you find this kind of construction as well, but they are subject of a controversial debate.
La vidì bevendo un caffè.
I saw her drinking a coffee.
The statement below is from a known Italian linguist.
"Di norma il gerundio condivide il soggetto del verbo finito al quale si collega (......). Diversità di soggetti può aversi.
a) Quando il gerundio si riferisce a un complemento oggetto o a un complemento indiretto. Si tratta di un uso frequente nell' Italiano antico e poetico. (......) Strutture del genere si incontrano anche in scrittori moderni (sicuramente quando tornerò la troverò piangendo. (....)"
"The norm says that the gerundio shares the subject with the verb with which he combines (....). But nevertheless a different subject is possible.
a) If the gerundio refers to a direct or indirect object. We find this kind of constructions in classic Italian or poetic Italian. (...). But this kind of construction can also be found in modern writers (When I am back, I will find her crying). "
Luca Serianni, Grammatica Italiana, Italiano comune e lingua letteraria, Turin, 1989, page 485
It is not difficult to find through a google search sentences, where the gerundio has its own subject. In general the subject is postponed in this case. Very often this kind of structure is an abbreviated causal clause.
Essendo lui malato la vita di colpo è cambiata.
Because he was ill live changed suddenly.
Avendo lui più di una famiglia, può essere considerato un buon cattolico?
Can he considered a good catholic having more than one family?
Abbiamoritenuto inopportuno una discussione, essendo Franco troppo irritato.
The discussion seems inopportune tu us because Franca was angry.
Besides that, there are a lot of idiomatic expressions which introduce a statement. A lot of these expressions have their own subject, even if this subject is abstract.
Parlando sul serio, tutti vogliono essere ricchi, ma nessuno vuole lavorare.
Talking seriously, everybody want to be richt, but nobody want to work.
Vedendolo così, anche lui sembra molto simpatico.
Looked this way he seems to be nice as well.
It is obvious that those who speak seriously are not the same people as those who want to be rich without working.
Besides that the gerund can have its own subject if there is no subject at all. The subject in a sentence in active voice is the executor of the action described by the finite verb, in a sentence in passive voice the sbuject is the goal of this action. But in the sentences below the subject of the gerund is just inexistent.
Piovendo così e meglio rimanere in casa.
If it rains like that, it is besser to stay at home.
Facendo freddo non si sarebbe sciolto.
If it were cold, it wouldn' t have melted.
A similar situation we have in time data like It is early. The it is a pseudosubject and it wouldn't cross anybodys mind that the subject of the gerundio is as well the subject of the finite verb.