[quote name='Wonky2' timestamp='1454272548' post='2968171']
Listen to them, A lot.
[/quote]
This^^
I usually play the next gig's material on random for as long as possible, wherever I go. For me, it's on my phone plugged into the car stereo. You might use a walkman or whatever. I sometimes drive the missus nuts by playing it at home; sometimes she really likes the tracks ('you're playing with this guy? He's really good!')
I rarely get round to actually playing the bass along with the listening, but by the time of the gig/rehearsal (do push for one of these) I'll have the shape of the songs in my head, so the actual key doesn't entirely matter. How many times have we done gigs where the singer says 'Oh, I don't sing it in that key any more; that was just on the album'?
Enjoy!