A verb can be added to an adjective as well, in English as well as in Italian.
In general it is better to lie than to tell the truth.
It is more fun to read a text than to write one.
It is better to do what you can't help doing.
In this case the same rules are to be applied as in the case of nouns. In general, the verb is connected with the preposition di and normally the preposition a is only used if the adjectives derives from a verb which requires the preposition a.
abituato = to be accustomed from abituarsi, to accustom
Sono abituato a dormire fino alle dieci.
I am accustomed to go to bed at ten o'clock.
destinato = intended from destinare = to allocate
Questo progetto è destinato a fallire.
This project is condemned to fail.
incline = from inclinare, to tend to
Il lettore è incline a considerare la notizia, per quanto crudele e triste, uno spettacolo.
The reader tends to consider any notice as cruel and sad as it may be as a spectacle.
tenuto = from tenere, to keep
Ognuno è tenuto a rispettare le regole di sicurezza.
Everyone is requested to respect the security regulations.
Besides that an infinitive can only be connected, in Italian as well as in English, if the subject of the finite verb is abstract ("It is difficult to say it to him"), the finite verb and the infinite verb have the same subject ("He is accustomed to sleep long") or if the direct / indirect object of the finite verb is the subject of the infinite verb ("I believe him being able to commit a murder").
the subject of the finite verb is abstract
È difficile fare sempre ciò che si vuole.
It is difficult to do always what one want to do.
the direct object is the subject of the infinite form