Gustar type verbs

You are not the subject of me gusta el café; the coffee is, and it is pleasing to you. So the verb agrees with what is liked: me gusta el libro but me gustan los libros. Changing I like to we like changes the pronoun, not the ending. Encantar, doler, faltar and quedar all work the same way round.

The a phrase in a mí me gusta repeats who is pleased, so it adds emphasis or contrast: a mí me gusta, pero a él no. With le and les it also says who you mean, because le can be him, her or formal you. The pronoun stays even then: a María le gusta, never a María gusta.

Me duele la cabeza is literally 'the head hurts me': the part that hurts is the subject, so the verb agrees with it. One part takes duele, two or more take duelen. Spanish says la cabeza, not mi cabeza, because me already says whose it is. Encantar, faltar and quedar work the same way.