Once you've got a gig, get a signed contract.
Club owners know how to take advantage of new artists and if you haven't brought in the sales, they'll play all kinds of tricks to get out of paying you. (ie, 'your soundman must have spilled beer on our board because it wasn't working after you left so we've deducted $200 to have it repaired'.. or 'no... I said I'd pay you $1000 for the whole weekend, not $1000 per day. You must have heard me wrong'