Hard to advice as each bar is different, not to mention every town/culture and even every evening is different. The only advice I could give you (but useless here since you are playing tonight already) is to go into the place a few times in the period before you have to play.
Experience, good people reading skills and a tight, not too big track collection that you know intimately are what usually get you through these kind of gigs.
It may help to realize that people are not there for you, but for drinks, laughs and contact with same or opposite sex others.
Actually it is pretty hard to totally screw up a bar night if you keep your eyes open and see what works and what doesn’t and act accordingly. Generally speaking I’d say that in a bar you have to have a wider range, be more popular track oriented (recognition is important here). You have less of an educator role here. Don’t bother working your set so you can introduce some new tracks you’ve discovered. If you want to play them, just throw them in and see how the crowd reacts.
Be willing and ready to abandon a direction you picked if you notice it’s not working.
Wish I could give you more concrete advice but unfortunately in my experience, these are “seat of your pants” nights.
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