I have no problem learning the instrumental part of a song, but I do struggle with learning lyrics. I've found that recording myself playing and singing the song, putting it on a CD, playing it over and over at home, in the car, wherever, and singing along with the recording works for me.

Although some people seem able to learn from written documents, it's a complete waste of effort for me, I find myself permanently reliant on reading the words but, by singing along to a recording, my brain seems able to lock the lyrics in.