Prepositions and infinitives.
I'm having difficulties understanding when to put "a" into a sentence after a conjugated verb but before an infinitive. I know things like venir require an a. Are these verbs just verbs without a readily apparent reason why that I'll just have to memorize?
For example, from another question asked on this site:
Estos son solamente algunos de los elementos que ayudaron a hacer de Volver una película popular, y (la cual) continuará entreteniendo a audiencias en el futuro.
I could have sworn I've seen infinitives used after a conjugation without any prepositions. Sé nadar. Now I know with saber there is an implied "how" in it like "buscar" has an implied for and only has an "a" if it is the personal a.
In some cases a is used and others it's not. These are basically for memory. Where you don't have to memorize is when using a verb that can relate a person or a thing. In theses cases, a is used with people, but not with things.
ie: Busco a mi hermana (I'm looking for my sister). Busco mi libro (I'm looking for my book).
Veo a ella (I see her). Veo mi casa (I see my house). Odio esa canción (I hate that song). Odio a aquel hombre (I hate that man).
I'm not certain that I understand the part of your example in in which you quote (I assume) "....ayudaron a hacer de Volver una película....". It appears that the person who wrote that wanted to say "bring back a popular film" in the sense that they wanted new people to see an old film. "Volver" doesn't sound right to me in that context. "Hicieron esfuerzos a que saliera de vuelta una película..." me suena mejor.
"Sé nadar" es correcto.
Don't think of "buscar" as "to look for" Think "seek" and you can forget the "for".
I always use "a" after "ayudar". Although, I notice, mostly in newspaper articles, that the "a" is omitted.