I was on the fence about putting the "dance" part in because I think a lot of people would try too hard and get it wrong.
But the most common newbie mistake is to, as a mentor put it, prostitute your product. They simply shove it into everyone's faces as loudly as possible. This works at a bazaar, but not in many places.
It's also a faux pas to wear a suit when approaching companies whose formal wear is a t-shirt. You don't have to find all the unwritten rules but just be aware of them.
If you know a bit of the formalism then just showing you are competent and have a solution to solve the customer problem is enough to start making deals. The rest is optimization.