Brade Goode is a great trumpet player who teaches at the University of Colorado in Boulder. I heard him speak about his transcription approach some years ago. It has been a long time but as I recall, his suggestion was:
* Pick a jazz solo you want to learn.
* Listen to the recording of the solo MANY times.
* Then sing along with the recorded solo until you feel comfortable that you know it very well.
* Then sing the solo without listening to the recording
* Then pick up your horn and play the solo .
* Then play the solo along with the recording to check your work
* The final step is optional: Write down the solo
I was once at a seminar given by Alto Sax player Jeff Clayton who suggested that you select a solo to transcribe that is within your capacity. His example (as I recall) was that for most of us, picking a Dizzy Gillespie solo as a first transcription piece might not be a great idea.