Clothes? That's actually pretty easy, but so many SB's mess it up, at least based on some that I've seen.
What is your personality type, and you body type? What are you trying to project? Classy? Comfortable and casual? Hopefully not slutty! But you will be surprised the percentage that show the latter.
Once you have decided your type and what you are trying to project, dress accordingly.
Don't have to overspend and impress, because chances are the SD has seen women in their fanciest attire already, and if he is really well off, he will not get impressed by that.
What will impress, however, is if you have succeeded in putting together the 'total package'.
Casual comfort is my favorite (but no faded jeans please, especially for dinner), and the right combo of jewelery, cleavage (just enough), and makeup.
By the way jewelery: I personally prefer none to very little.
Chances are (no offense) you may not be able to afford the same jewelry he gives his wife so don't even try.
I think a simple ring or bangles are enough.
But it has to match, again, the rest of the clothing, and not be too loud.
Shoes: Many SB just love Louboutin's.
Sure they look nice.
I don't really like them, I must confess.
You know what? I am the casual type that's why.
But anyways, being a man, I will stay away from comments on women's shoes, LOL.
Show confidence.
I believe that's more important than the actual piece of clothing you end up wearing! Just my opinion...