I used to go pub crawling a lot, and dancing whenever I could. I still do the hipster bar thing weekly.
What Anna says is great for a casual bar, wear jeans that really look great on you (avoid bling if possible as it is distracting looking), and shoes that are comfortable to walk in but make it easy to walk or dance. I usually went with boots or booties that elongated my legs because of the shape, the color matched the jeans, or they had a bit of wedge heel or something.
If it's a step up from a dive bar (which is tee shirt and plaid zone) I'd wear a flowy top in a good material that drapes in a flattering way, or shows off your arms or something and is a good color on you.
When I wanted to dress more sexy I usually picked only one area that leaned that way a bit, like a drapey shirt with either a wide low neckline or bare shoulders or something. Or I'd wear a black turtleneck sweater and high black flat boots and tights, but a metallic miniskirt or something. Keeping it subtle and understated made me feel great wearing it - attractive and strong.