Learn Italian: I biglietti? Dovete stamparli prima del viaggio. - The tickets? You must print them before the trip.

When you have a modal verb like dovete (you must) followed by an infinitive like stampare (to print), you can attach the object pronoun directly to the end of the infinitive. Notice that we drop the final -e of the infinitive to do this: stampare + li = stamparli.

Can I put li before the verb instead?

Yes! With modal verbs like dovere (must), potere (can), and volere (want), you have two choices. You can attach the pronoun to the infinitive (Dovete stamparli) or put it before the conjugated modal verb (Li dovete stampare). Both are perfectly correct and mean the exact same thing.

How do I know to use li here?

li is the direct object pronoun for "them" when referring to masculine plural nouns. Here, it refers back to i biglietti (the tickets). If we were talking about a feminine plural noun like le carte (the cards), we would use le and say Dovete stamparle.

Why is it prima del and not just prima di il?