Sadly I now view myself at somewhat of an expert in first dates (!) as I've probably gone on more than the average person. So what to wear on a first date?
1. Finding a balance between feeling like you look nice, and feeling comfortale. Nothing worse than worrying about your skirt riding up, or falling over in your shoes.
2. Finding a nice balance between looking like you've made an effort (I once went on a date with a guy who wore shoes with holes in), and not overdoing it. I tend to not wear bright lipstick on first dates for this reason. I find a dress, but flat shoes work for me.
3. Setting the tone for your expectations. I reckon I'd wear something different if I was looking for a cheeky one night stand.