kind of depends on your intent.
If it's to learn a tune, then you only need to transcribe the chord changes and the melody. The melody is usually easy.
The chord changes can be trickier, depending on the kind of music.
Start by transcribing the bass (if any), which usually contains the root and the 5th on beat 1 and 3. If you get that, it becomes kind of easy to figure out which general group your chord is in
Major, minor, dim or half diminished.
if your intent is to learn a solo, say Van Halen on "Beat It", then something like Transcribe! will save you hours and hours.
You slow it down, listen carefully, play it along with the dude, on your instrument, at 50% speed, or whatever is comfortable. Do that 1 bar at a time. If you play it with the soloer, you will
- Commit to memory really quick
- Learn not just the notes, but everything else that applies to the instrument
You don't need to take the word "Transcribing" literally, it's up to you if you want to write stuff down.
I do if I transcribe a leadsheet or a riff, I don't if I transcribe a solo.
Transcribe stuff you can actually play, at some kind of reasonable speed.
And Transcribe only the really good guys on their really good days.
hope this helps.