I have been playing for years, and it took me a long time to develop my ear. But, I wish someone had told me at the start, the same advise I give, which is ...Make sure your guitar is tuned properly to concert pitch (via a electronic tuner). Then just put your fingers on the strings, usually G string, and while listening to radio, cds, tv etc, and slide along until you hear a note match. There is your start. As you learn blues (& major) scales, The patterns that is, you play around with the shapes, around the notes you know are contained in the song. Also if you find the correct fret to play the root6 bar chord, and or the blues scale pattern, (or major/minor) remembering that the 1st string E, and 6th string E, can help identify the key. You must start learning the scales, (mainly blues, and major). Not necessarily note for note, but the patterns they create, and positions on the frets.
Also the relative minor relationships can be handy for chord work. IE an Am chord,&is the relative minor of a C chord, and sound similar. The interval between C & A is a 6th, i think. G & Em, D & Bm, F & Dm are some others from my depleted memory. They can be worked out for every Major Chord. I picked up notes first, now try chords, and have better success than I used to. Just keep trying, and it will come....believe me !! I hope this helps Tony