Use some toolsFirst, I advise you to install on your computer a DAW (Digital Audio Workstation). It will allow you to slow the music down, and apply some effects to change the sound of the song (EQ, compression, etc). You will also be able to replay the most difficult parts, and add markers to identify the different sections. I personally use Reaper, but you can use one of your choice (Cubase, ProTools, Audacity, etc). There are other tools that can help you, although I personally limit myself to the DAW. Note for example Transcribe! Which determines the frequencies heard at a certain time and then the corresponding notes.
Define the structure of the songThe first step is to determine how the song is structured, which means defining the different parts that compose it, and the number of repetitions of each of these parts. To do this, take a sheet of paper (or use your computer) and listen to the whole song. During playback, you will write down a line for each part. When a new section begins, write down its name on a new line (for example, "intro", "verse", "chorus", etc). Count the number of repetitions of that part, then when the part finishes, write down the number of repetition next to its name. Here is an example of song structure (basic): intro (x4) verse (x2) chorus (x1) verse (x4) chorus (x2) Solo (x1) chorus (x2) outro (x1) Doing so you will help you later to see where you are in the progress of transcription, and it will also help you when you will write the corresponding tab.
Find the notes playedThe technique is the same whatever part of the song you study. If you have no idea of the key note of the song, listen to it, and play on your guitar all possible notes (12 in total on the fretboard). Note that some of them sound nicely with the music and other sound bad. Note down those that sound good. They will be the ones most likely to be played in the song. From these notes, we can begin to find the real notes played. Start studied part from the beginning, and try to find the first note played. For now, do not try to find a complete chord, only focus on finding the notes used. When the first note is found, find the next one, and so on. I suggest you write each note found, not to forget them along the way! Once you have determined the notes played, you can find what chords are played (if there are chords). In metal music, most of the time there are power chords, composed of the root note and its fifth (for this reason, the power chord of, for instance, E, is named E5). Beware though, in hard rock more complex chords are used. If you do not find any chord corresponding to the one played, try to play all chords corresponding to the fundamental, you should find one that sounds the same as the one you are looking for. As for solos and fastest parts, don't hesitate to slow down the music with your editing software. You can also write down the scale (or look for it on the Internet or GuitarPro) so you'll see which notes are most likely to be played. Also remember that you have the right to improvise during the solo, you're not forced to play a 100% identical solo!
Find the rhythmFor some people, this stage is natural and if you're one of those people, you have at this point already found the right rhythm for each note. For other people, it is not so easy to play over the song with the good rhythm. If you can not find the duration of each note, start by slowing down the music, so that each time lasts longer. This way, you will more easily be able to count both the black notes, but also the divisions of this time. Another tip is to tap (with your foot, your hand, whatever you want) on the tempo (or even 2 times faster than the tempo when the tempo is slow). You will hear that some notes fall right on time, some other right between two times, and some fall at quarters of time.
Write a tablatureThis step is not mandatory, but is recommended if you do not want to forget the song over time, and thus lose all your transcription work! And also because here we are on a website that gives you tons of good user tabs, so it's a good idea to post some of your own tab to help other people! You can either choose to write it by hand or using specialized software. If you write it by hand, you can find on the internet empty tabs (which only contains the lines corresponding to the strings), print them and then add notes on top of it. If you prefer to write on a computer, you can use a specialized software like GuitarPro or TuxGuitar. For more informations about how to write a GuitarPro tab, you can check the tutorial I have on my blog (link below). Have a question about this lesson? Got a problem? Post a comment, I will answer! Here is my blog for more tutorials.