Here are some off-the-wall ideas for training your ears:
For semi-advanced practitioners.
Use a tuning fork to tune 1 string. Then tune by ear.
And/or use a good quality recording of your instrument when you know it is perfectly in tune, or a piano or other dependable instrument to fine tune by ear. Like a good teacher might do at the beginning of each lesson, just playing the proper notes for you to locate.
Or use an electronic tuner to get one string in tune and try to tune by ear.
I guess the obvious point is to try tuning by ear, every time, in an attempt to do it better each time, and therefore you will get better and better at it.
Then use the best electronic tuner you can afford to check your ear.
Then practice intervals in unison while singing the notes along with the instrument.
Spread out the harmonics by singing chord tones along with your instrument. For example practice singing 3rds in between a root and a fifth.
Practice semi-tones, note bending, various harmonic relationships around a droning note. Using your voice in harmony with the many voices of the Megatar.
Optional: Work on one "Key" for an extended period, like a week or longer, such that you really start to inhabit the space that is "The key of D major" before moving on. Take on the scales and the intervals, progressions, try some songs in that key, identify recordings in that key and jam along. Pick up licks and ornaments in that key.
When you get full of that key, put down your instrument for a few days to let it soak in. Then get back at it in another key.
Do these things and your pitch will get better.
With disciplined practice one will quickly achieve the ability to tune by ear, and with more practice one will be able to identify notes, intervals and harmonies.