I am 2 years into playing bass and I am very much still trying to figure out the best approach to combine speed and accuracy. I played covers with guitar in the past for a long time, but for some reason things don't work the same for me with the two instruments. Here's a bunch of thoughts I am gathering from my current understanding about what kinda works for me...
1) Faking is ok
I am very much a note-for-note fanatic, but it's a recipe for long and hard work. Almost nobody will really notice if I play as on the record or something different, in 99% of famous songs, people only really notice the vocals and the main riff (which is usually guitar or keyboard). On a minority of songs, there can be a legendary solo, almost always by the guitarist, which can attract scrutiny.
Obviously, the core bass groove is very important, and I would never fake that. But it takes very little time to identify the core bass groove of a song, what takes me most time is figuring out the variations on each measure (hearing them properly from the record, writing them down, finding the best fretting and fingering, practicing them technique-wise and finally memorizing them!). To get ready for rehearsal/gigging as fast as possible, in the first stage just nailing the grooves in each section goes a long way, takes 1% of the time and delivers 90% of the song!
Some songs seem to actually require some bass variations to feel good, but it doesn't have to be exactly the same variations of the original recording. So if you feel some songs are too boring when repeating the groove always identical, your second stage could be to either (1) identify chords and improvise your own variations, if you are good at that, or (2) write down a few of the original recording variations, learn to play those few but apply them on the spot whenever you feel like. This is a bit typical of drummers who learn a vocabulary of "my own fills" to use randomly when the song has a moment of emptiness e.g. because there's a gap in the lyrics.
If faking leaves you a bitter taste, you can always tell yourself that this is only to get there as soon as possible, once you're rehearsing/gigging you can always improve the accuracy against the original later on
2) DIY helps
Transcribing by ear and writing down your own transcription are proven processes to commit to memory much better, but they are of course time-consuming, so unless you're quite good at these already, I wouldn't recommend to all the hard work. Which is worse, spending 10 hours to transcribe a 3-minutes song to have it almost memorized by then, or spending 10 hours memorizing it from someone else's the transcription? Clearly, the answer is 'neither'. There is most likely a combination of things that leads to being ready faster, but which one is it isn't obvious.
What I normally do, is to always start from an existing transcription if available. In order from the fastest method (for me) if a transcription is available, I use Rocksmith, followed by YouTube, followed by UltimateGuitar, followed by official TAB books. Here I don't necessarily mean 'fastest' for achieving results, but 'fastest' as in 'if there's a transcription for this method, I'll be up and running practicing it in a shorter time'. For example, official TAB books are much more reliable and accurate than all others, but before I order one of those books it'll be days at least... with Rocksmith it takes me a couple of minutes to start, with YouTube I need to typically at least vet a few videos to understand which are decent, and with UltimateGuitar I need to wade through a lot of garbage.
But whatever the starting point, I always work my way back to fixing the mistakes in those sources in a second phase. You'll notice glaring mistakes quite immediately, and subtle ones perhaps later on, but your ears will always be the final arbiter. For some reason, I am much better at spotting mistakes in other people's work than mine, so if I transcribe something from scratch by myself, it might take days before I notice I got something wrong, hence my habit of starting from an existing transcription and work backwards.
The other DIY mechanism that really helps (with memorization) is writing it down. It takes time on its own so if you're in a rush and you already have a written transcription, just use that, but when your purpose is committing to memory, even just copying a score with a pencil on another empty sheet will help with the memorization process.
3) Focus rather than multitask
I have the tendency of making this mistake all the time
but don't practice too many songs at once. If you have for instance a week to learn 5 songs, it's ok to give all of them a first pass on the first day (at least to get an idea on how hard each one is going to be), but then try to stick to one song at a time, for example limit yourself to 1-2 songs per day. It depends of course how many hours you have on each day, but at least don't jump from one song to the next too quickly, in the transcription case try to fully transcribe one song at a time, and in the practicing phase maybe replay each song ~10 times in a row rather than 10 songs one time each. Focusing helps both making it easier to play and committing to memory.4) Work from the easiest to the hardest
I have debated this endlessly since I was in school... some of my schoolmates used to always tackle the hardest homeworks first, so that the worst is done and got rid the sooner. The danger of that is, should you failed to finish the hardest homework, you'd have no time to do the easiest ones either.
So if I have a list of things to do, be it songs to learn or work tasks in my daily job, I always start from the easiest so that I can check many off the list quickly. If my boss sees my checklist near the deadline date and sees almost everything done except the hardest task versus seeing everything undone "but I am almost finished with the biggest task, and I'll do all the others tonight", what do you think it's going to make him feel more comfortable?
If I got 20 songs to learn, and there's a chance I won't make it with all of them, I'd rather have the easiest 15 ready to gig than the 5 hardest ones, very simply!
(no offense, of course).
