Everyone that can hear normally has the ability to train their ear. I've taught dozens of students that claim they "just did not have an ear", and yet after few weeks of lessons they are able to start noticing when their guitar is out of tune.
It happens relatively quickly once you start hearing how things are supposed to sound.
Training your ear is like training your fingers on the guitar, it takes repetition, and it takes accuracy. Tuning your guitar every time you play is the simplest and most natural way to teach your ear what sounds good and not.
There are some excellent tools you can use in addition to just tuning your guitar regularly. My favorite is the Advanced Ear Training Software for musicians from Jana Software. For more about Jana Software make sure to check out the information on our main website.
Another strategy it to listen to your favorite recorded music. People tend to hear the music, what I am talking about is listening to the music. Focus on the sounds you hear and how they change. How the tones go up and down. Don’t worry about what key the song is in, or what notes is being played, just focus on the tones.
You do not need to be concerned about music theory or music notations to learn about how sounds relate to each other. It truly is a natural instinct, when two notes are played together that sound good, you know it, and when they sound bad, you know it as well.
Do not let your inexperience with theory keep you from doing what comes naturally with the experience of just listening to music, and the notes you are playing on your freshly tuned guitar.
With time you’ll notice how sensitive your ears become to sounds that are not “right” and you’ll be able to instinctively reach up and adjust the tuner to make it sound right again. It takes time, accurate repletion and a desire to want to ROCK ON!