Hi Demon!!!
First of all train all the time any song you have in your mind go to your bass guitar and try to play it. Don't try to find only the Bass lines but also the melodies of the singer.
Start with easy stuff like kids songs and move forward to harder stuff once you feel you can get the easy stuff easily.
Second. try
This Website It's good for all theory stuff but it also have Ear trainer for Intervals , Scales and chords, this can help you a lot on your way to have good musical hearing.
Good luck.
Salute
Adi.