Use of prepositions between verbs, a, de etc.
When linking two verbs, usually the first being conjugated and the second in its infinitive form, sometimes I note you don't need a linking word whereas sometimes you do, and the linking word changes, depending on the first verb. Are there any rules for this or it is simply a case of memorisation for each verb ?
- Quiero hacer........... querer doesn't need a linking word
- Empiezo a hacer..... empezar takes 'a'
- Acabo de hacer....... acabar takes 'de'
5 Answers
Adding to what txustaboy said:
WE probably have many more idiosyncrasies in English that native speakers never think about
We grow up with them and there are no "rules" to follow - we just know when they are not correct.
PS
The only aspect of English grammar that I know has no "exceptions that prove the rule" 
are the Modals.
I´m sorry to say that you have to memorize each particular case. Besides, there are some cases in which even a lot of Spanish people have problems to build the sentences using the correct form.
So, you should memorize the most typical cases and each new case you see.
Maybe in "Acabar de", "Empezar a" and cases alike it'd help not to see 'acabar' just as a verb that takes 'de' when conjugated and placed in front of an infinitive. Instead, try seeing it as part of a set of syntactic expressions called 'Perífrasis Verbales', especially because the conjugatable verb tends to change its meaning (tener-->tener que) and some verbs can even take several different prepositions, or none. Specially for you, I will list 15 of the most frequently used ones and provide some typical examples. :D
Infinitive:
Obligation
HABER QUE (general obligation/advice, without reference to a specific person) "Hay que llegar a tiempo (a la boda de mañana)."
TENER QUE (obligation caused by the situation) "Tienes que subir por las escaleras rojas."
DEBER (obligation set by the speaker) "Debes acostarte ahora, hija."
instead of using a different time
IR A (i.p.v. futuro) "¡Voy a volverme loca si no dejas ahora!"
DEBER (DE) (i.p.v. futuro/condicional used to guess at something) "Deben (de) ser más de siete."
ACABAR DE (i.p.v. pasado, used to say something júst happened) "Acabo de entrar, ¿¡¿qué está pasando aquí?!?"
start, stop and do again
PONERSE A (start) (your 'empezar a' goes here, too )
"A ver si te pones a trabajar."
DEJAR DE (stop) "Deja de hacer tonterías, chico."
VOLVER A (do again) "Te prometo que no volveré a hacerlo, mamá."
Participio
SEGUIR (continuous situation) "El coche sigue estropeado."
TENER (completed action, usually with concrete result) "Ya tengo compradas las entradas."
Gerund
Continuing action
SEGUIR (general continuation) "¡Sigue leyendo tú, Elsa!
IR (slow development) "La situación va empeorando cada día."
Ending action
ACABAR (close off/finish by doing ..) "Siempre acabas diciendo que no!":(
LLEVAR (how long .. has been going on) "¿Puedes creer que llevamos cinco años viviendo juntos?"
I made the examples up and I'm not a native, but I think they reflect the intended meaning pretty well. Source: my notes from my Spanish grammar class.
Your "quiero hacer" is a different case entirely. Here, the conjugated verb uses its most common meaning, and it might be useful to note that in this case, both verbs refer to the same person, ALWAYS.
If not, instead of using the infinitive, you use a subordinate clause, (in which you have to be on the lookout for the subjuntivo!) For example:
"Quiero jugar al fútbol contigo." vs. "Quiero que juegues al fútbol conmigo."
"Prefería ir a la playa sólo." vs. "Prefería que te fueras a otro lugar."
"¡Mamá, ya tengo 5 años, puedo vestirme yo!" "Bueno, si de verdad lo puedes hacer, prefiero que lo hagas tú, entretanto puedo maquillarme."
I'd say this is the most common way in which an auxiliary verb is used; without a preposition. If a verb takes a preposition, this is always mentioned right next to it in the (online) dictionary. It's a matter of getting used to that takes some time when learning any language. Take this for example:
'to dream about' = 'dromen over/van' (Dutch) = 'soñar con'
I find that these differences are one of the interesting ways in which a foreign language shows you another way to perceive the world. "to dream WITH"? Hey, that makes sense!
Buy a 501 verbs book. In the back is a list of most of the verbs that need a preposition. It is more than 20 pages long in my book. No way to memorize them. They will come with usage and errors. Like Suzy said concentrate on the ones that match up with things you would say in English. If you don't use the verb in English you probaby won't use its equivalent in Spanish. After all, our speech patterns are formed.
