Music starts with your mind, which means music theory. There is no way around it. If you don't have the music theory in your head, then you just gonna be playing by ear, and you won't get very far just playing by ear.
You need to first know every single note on your keyboard. You should know every single white key and black key anywhere on the keyboard.
Once you got that, then dive into learning your major scales. There are 15 off them total and you should be able to recite them and their members w/out looking at a keyboard. Then when you get to a keyboard, say each letter of the scale first then play.
Next, move on to your basic chords: major, minor, augmented, diminished
chords. As with the major scales, you should be able to recite them and their members w/out looking at a keyboard. Then when you get to a keyboard, say each member of the chord first then play. This goes for each of the inversions and for every key also.
Next, move on to progressions. I have the progression posts on here so you can look for them by searching. Practice each progression in every key as much as you can.
Once you got a good handle on progressions, then listen to as many CDs as you can and start listening for 2-5-1s and 7-3-6s. Listen for familiar chords that you know and try to play along if you can.
Tips: As you are going through each of the above exercises, pay very close attention to how everything looks and sounds. If someone is playing
a major scale, you should be able to tell by sound if it is indeed a major scale. This goes double for the chords and progressions. You should be able to tell and hear the difference between a major chord in root position and a major chord in 2nd inversion. You should be able to spot a 2-5-1 progression or a 7-3-6 progressions in a song by ear. Like I said before, music starts in the mind so you have to train your mind harder than your fingers.
