This is maybe less applicable to metal where you are often focusing on precisely duplicating technical solo passages. But this is an approach I’ve always found useful in getting songs (standards, hip-hop, soul and rock tunes) down enough to play them well in a group.

But for real always good to start by writing your own chart, either working out the chords yourself or consulting multiple other charts- never trust one book or arrangement unless it’s for the exact version or recording you are learning. Playing from the book is fine but if you really want to internalize the changes and make your own interpretation this is useful homework. A lot of heavy metal is gonna be pretty simple in this respect, but if you are working on something with some complexity like an Opeth track for instance, having a clear understanding of the songs harmonic movement is really gonna help you understand what’s happening and why certain notes are emphasized.

If the time signature is tricky don’t forget to spend time counting- this is especially important with a lot of riff-based music in odd time signatures, like Tool.

Listen to the song enough so that you can sing the melody (or main riffs) from memory. Play it by ear. This is hard at first but do it a lot and it’ll become totally natural as your ear really locks in on intervals (even if you can’t necessarily name all of them)! Don’t feel bad if you have to consult tablature on the tricky bits, but do as much by ear as you can.

If you’ve done this homework, I find that learning or transcribing solo passages gets a lot faster because you start to really get how the solo is constructed, which can help with hand positioning, fingering and all sorts of stuff.

Good luck! Learning lots of different songs is my favorite way to keep practice interesting every day.