Reddit mentions of Ear Training for the Contemporary Musician

There are formal methods for ear training.

Auralia is popular software used by music schools, usually as a supplement to aural skills classes.

A good book on the subject that is less classically oriented is Ear Training for the Contemporary Musician.

Most methods start with sight singing, which is a good way to internalize intervals without thinking about key. Then you move from those skills to interval recognition, and after getting decent at that you can do melody recognition (melodies are just a bunch of intervals in a row). After a little bit of interval training you can have a go at chord recognition.

So, start just by practicing with simple melodies that you know by heart: christmas carols, nursery rhymes, movie themes, that sort of thing.

It'll require a lot of hunting and pecking and will be slow, but that's fine.

Then I would start working with the functional ear trainer. It's a free download from miles.be - again, it will feel crazy difficult at first, and that's fine. Stick with it - 5-10 minutes a day, five days a week.

If you want more, you could get a book on ear training. I recommend this one: https://www.amazon.com/Ear-Training-Contemporary-Musician-Elliott/dp/0793581931/ref=sr_1_1?ie=UTF8&qid=1502376335&sr=8-1&keywords=ear+training+for+the+contemporary+musician

Although in my opinion, you should start with the other two things.