Learning to fault find is a barrier you're best of pushing through on your own by gaining your own experience. You can act on advice by others, but the fault finding work itself has to be your own. It takes years to gain a good fault finding skill and it's all about experience, electronics knowledge, and commitment to keep going even on the really tough faults!
Unfortunately, the Electronics Diagnosis trade is in such a state these days that companies no longer feel that they need to pay for a fault finding skill. Even though the skill takes years and years to learn, and is subject to an in depth Electronics background, they still don't feel the need to pay for it and in some cases, they don't need to anymore!
Brian