Well, first of all, I would reccomend new strings if your old ones sound so bad. I like Dean Markleys but Ernie Balls seem to have a better sound but I don't like them too much since they break easily. At your stage you can keep learning other peoples songs unless you want to start making your own. If you want to make your own then I suggest that you get books on theory and learn as many scales and chords as possible as this will help you get started on understanding how they work. What kind of amp do you have? I might be able to help you.