I'm gonna have to agree with the ppl who have said learn scales and thoery, also work on your ear from the very begining, that is something I wish I had started much sooner than I did. Also learning songs doesn't really help you learn to write songs unless your just going to rip everything you write off someone else, I no only know two songs all the way through, and that is only becasue they are strumming songs that repeat a four bar pattern the entire way thorugh except for the chorus which is a slightly different four bar pattern. I spent he first year of my playing learn scales and practicing them like mad, litterally playing up and down the penatonic scale for hours, getting my fingers used to moving around it. Then I moved on to modes and more complex ways of playing (I was also working on techniques like pull offs, trills, ect.) all the stuff I knew, I learned lots of theory which I am still learning. If I want to learn more about writing music it's very simple, I listen to music, I dont need to learn it because I know what they're playing and why they are playing it.

It is also nice to be able to get the key of a song in just a few seconds. It helps to know about the genre your dealing with too, even right down to the artist your dealing with. Almost all rock songs are writen in A, E, or G and they almost all use the pentatonic scale prettty heavily.

That said if your going into a cover band for some reason ;) just learn a bunch of songs you like, all the way through, but also learn scales, particularly the pentatonic and blues scale since that will help you to make your solos and such original rather than just ripping it off the artist your covering.