Here are the basic steps I go through to learn a new song:
1. Find the key
2. Figure out the bassline
3. Figure out the melody
4. Fill-in the middle
As I am listening to songs, I listen for familiar chords, progressions, runs, scales, basically anything that I have heard before. When I hear a part or the song or chords that sound familiar, I start right there. Don't matter if it's at the beginning, middle, or at the end of a song. You got to have somewhere to start. It's just like a math problem, first u write down what u know, then figure out what u don't know. You will rarely run into a song where nothing sounds familiar. There will always be something you have heard before cuz music is universal. I have gotten to the point where I don't really need to write stuff down anymore, cuz I do the work in my head. But, for beginners or anybody, I suggest writing it down on paper.
A lot of people don't realize it, but there are no short cuts to learning music. It takes hours and hours of going over the same boring stuff. Major scales, progressions, chords, basslines, etc. even I get tired of playing them, but i keep doing it. It will get easier, trust me. If you need help with a particular song, then just let me know and I will do my best to assist you.