69 Dart 340 Info Needed

Hi guys I am getting a 69 dart with 340 motor and everything is stock in this dart.And i would like some info on what it is I can do to this dart to get more HP and if possable better gas milage..You snickered at the better gass milage didnt you...Well I am just curiouse as if these two things I can do with as little cost involved as possable..I am going to be using the dart for town driving and the acational street race..So if you can help me out as if you were talking to a nebie that would be great...Thanks...Steve