Combination of pronouns
Have a look at the following examples:
| (Lui) mi invia un´email. | He´ll send me an email. | 
| (Lui) me la invia. | He´ll send it to me. | 
| (Io) ti offro un caffè. | I´ll offer you a coffee. | 
| (Io) te lo offro. | I´ll offer it to you. | 
| (Io) gli mostro un quadro. | I´ll show him a picture. | 
| (Io) glielo mostro. | I´ll show it to him. | 
| (Io) le mostro un quadro. | I´ll show her a picture. | 
| (Io) glielo mostro. | I´ll show it to her. | 
| (Io) Le mostro i quadri. | I´ll show you the pictures. | 
| (Io) Glieli mostro. | I´ll show them to you. | 
| (Lui) ci mostra una rosa. | He´ll show us a rose. | 
| (Lui) ce la mostra. | He´ll show it to us. | 
| (Lui) vi mostra le riviste. | He´ll show you the magazines. | 
| (Lui) ve le mostra. | He´ll show them to you. | 
| (Lui) gli invia una lettera. | He´ll send them a letter. | 
| (Lui) gliela invia. | He´ll send it to them. | 
Notes:
As you can see from the examples above, if there are two object pronouns in a sentence,
- they both precede the noun, the first pronoun being the indirect object pronoun and the second being the direct object pronoun.
- i of the indirect objec pronoun changes to e
- pronouns of the 3rd person singular and plural (gli, le, Le) + lo, la, li, le are written together as one word
- Le refers either to a man or a woman when addressing somebody formally
Pronouns with modals
With verbs potere, dovere, volere there are two possibilities as for the position of the pronouns.
Compare:
| Voglio offrirti un caffè. | I want to offer you a coffee. | 
| Voglio offrirtelo. / Te lo voglio offrire. | I want to offer it to you. | 
| Devo mostrarti un quadro. | I must show you a picture. | 
| Devo mostrartelo. / Te lo devo mostrare. | I must show it to you. | 
| Puoi farmi un favore? | Can you do me a favour? | 
| Puoi farmelo?/Me lo puoi fare? | Can you do it for me? | 
Notes:
- As you can see, when we add a pronoun to the infinitive, the final e of the infinitive is dropped.
- As for the position of the pronouns in the present perfect (passato prossimo), click here.