Many Spanish verbs need no preposition before an infinitive.

Merecen ser libres.
They deserve to be free.

However, some Spanish verbs require a preposition before an infinitive. The following list shows the prepositions needed to link some common verbs with the infinitive.

Sueño con viajar.
I dream about traveling.

Verbs marked with an asterisk (*) take a for all direct objects, not just the usual “personal” a (e.g. Ayudan al desarrollo).

Verbs of motion such as ir, bajar, entrar, etc., always use a before an infinitive for destination, and de for origin: Vengo de hacer compras. Subió a ver al médico.

*animar a (algo) - encourage to           acusar de - accuse of 

*ayudar a (algo) - help to                cesar de - cease from 

*condenar a (algo) - condemn to           comenzar a - begin to 

consentir en - consent to                 convenir en - agree to

consistir en - consist of                 depender de - depend on 

*contribuir a (algo) - contribute to      empezar a -  begin to

cuidar de - take care to                  forzar a - force to

*desafiar a (algo) - challenge to         impulsar a - urge on to

dudar en - hesitate over                  insistir en - insist on 

enseñar a - show how to; teach to         llevar a - lead to 

*incitar a (algo) - incite to             invitar a - invite to 

*obligar a (algo) - oblige to             mandar a - send to

persistir en - persist on                 pasar a - go on to 

*persuadir a (algo) - persuade to         terminar de - finish 

presumir de - boast about                 tratar de -  try to

quedar en - agree to (used informally)    soñar con - dream about 

*renunciar a (algo) - renounce            *tender a (algo) - tend to

volver a (hacer) - (do) again 

acabar de: acabo de estar ahí - I’ve just been there
 
dejar de - leave off, stop doing something