I've got a sideman gig this Saturday for which I had to learn about 20 songs.
No problem, you say.
Except right on the back of it is another show the following Saturday where I need to learn 55 other songs!
So, I'm cramming right now!
1. Immersion and repetition, get all the songs on a Spotify playlist or whatever and listen to them (and nothing else) as much as you can. I even fall asleep listening to them, I wake up and they're still playing. It also leverages your subconscious to do some heavy lifting in terms of processing.
After repeatedly listening you stop listening as a fan/spectator and start to listen more objectively. This helps you build an understanding of the song structure and more importantly helps you to deconstruct the various parts.
2. Check if anyone else has already done the work. Shortcuts are fine - if they maintain the quality of your playing - I'll check out Justinguitar or Shutup and Play or some other lesson resource on YouTube - but only if it's accurate. By now I'm so familiar due to point A, I can evaluate this.
3. Live performance reference by original artist, especially for consolidating multiple guitar parts or for an arrangement with live instruments that differs to the recording. This can also reveal open tunings, drop tuning and capo usage.
4. Chart / Tab the Song. I do this by ear. At the end of this process I rarely end up referring to the charts because the process of listening hard and personally writing out a chart or tab that helps embed the song structure and cues so well. I also might not tab an entire song, just the key intricacies.
I might check my tab against a tab online but to be honest, most of them are so poor that I haven't often found it beneficial.
5. Use LIFI. I use the LIFI technique (Last Input / FIrst Input ) to help solidify the learning of guitar parts quickly. LIFI works by playing of the guitar parts just before you got to sleep. (the Last Input signal to your brain) and playing them again as soon as you wake (First Input signal).
6. Play the song in a context band as soon as you can - like that night if possible. Failing a full band rehearsal, get together with one other member who knows the material better than you. Check for arrangement alterations, how songs are ended live when they fade out on the recording etc
7. Take time off for the the input to percolate Give yourself a day of not working on the songs, allow you brain to catch up and solidify the learning, you'll find it better when you come back to it.
8. Play across the transitions Don't just do verse and chorus. Do half the verse into the chorus, cos these transitions are the periods when the brain goes "Er, what's next again?...... oh yeah". Playing across the transitions between each section helps smooth that shit over nicely.
9. Play Live without a Net test your recall with a rehearsal with no chart/tabs. No stopping after stuff-ups and no going back to the beginning. Play the song all the way through in one go (regardless of errors) then repeat, and repeat.
PRO-TIP: Get your singer to learn the song, not read the lyrics of their f*cking phone, because otherwise they end up not knowing the structures and at the gig lead you straight into Chorus 3 when there's supposed to be a solo and a breakdown first. (but it doesn't indicate this on the lyrics)