Fake chord or lead sheets and play the chords shown, i.e. make up the bass lines you think will work best with the chord used. Take all that knowledge you have stored up and put it to use. Your goal is to play with others.
And yes get a music stand and play with the sheet music on the stand. When you start getting paid for the gig then it is expected that you leave the stand at home. After awhile you will only need to peek at the chart.
I never did like playing by rote, (tab or standard notation) and I can not nail the chord progressions well enough to count on play by ear - except in a jamming circle where close enough is good enough - so fake chord seems to do what I need. We keep over a hundred songs in our active gig book and I can not memorize 100 songs.
Give fake chord a try. Google -- guitar chords, "name of the song" the comma and quote marks help in the search. Re-type what you find using large font and as I think in interval numbers I use the Nashville numbering system, i.e. I-vi-IV-V7, instead of chord names, i.e. G-Em-C-D7. Never know what key the vocalist wants so the Nashville numbering system works best in this case.
http://en.wikipedia.org/wiki/Nashville_number_system Yes I use Roman numbers instead of Arabic - your choice.
Good luck, start composing your own bass lines.
I have some tab stuff but it doesn't sound the same as what's being played. I know there's no cut and dried procedure here but when I try to play along with a tune, I can't follow it and then get discouraged and stop. Sounds like a bunch of 
. I know.
By the way, auditioning for bands is a great way to assess your current abilities.
