I had the same problem with my horse who was very buddy sour and I was a beginner as well so it was tough at first. I really like Clinton Anderson's methods from Downunder Horsemanship and watch him on RFD TV network. Ground work has made a big difference for Jasmine and I. Once we went back to ground work and did exercises such as free lunging in the round pen, lunge lining, yielding the hindquarters, etc she is much more respectful. Moving their feet around basically re-establishes your place as dominant in the "herd" and causes them to respect you more and moves their herd buddies down the list.
Also when riding, start with a buddy and do small exercises close to the buddy, and with each lesson, start moving them farther & farther away. Be sure to reward the smallest try. As progress improves, make sure you ride as often as possible alone. Jasmine really had to get used to it as most often we have to ride alone since we don't have many around who like to ride. She still has her "off" days where we can't get too far from her pasture mate, but even on those days, I push her just enough out of her comfort zone for her lesson, but not too far that she expodes, and then reward her for her efforts.
I have also found it helpful to do lunging for respect exercises on the lunge line near trouble areas such as her spooky areas of the pasture which tend to make her more nervous and this has helped too.