6. Know your product
Nothing is worse than watching a vendor squirm when asked about product specifics. "ummm...", "uhhhhh..." Buzzkill. If you don't know your product, then you don't believe in it.
7. Know the bugs in your product (and work around them)
If you appear surprised by a problem, it screams out loud that you didn't prepare or don't know your product well enough. Most software products have "known issues", if not by the public, almost always by the vendor.
8. Know your competition
Customers are almost always going to throw a question at you about whether your product can what the other vendor product can do. Know the answer beforehand.
9. Know the market pricing
You cannot pitch "value" without having the sum of features/pricing. If you can't do that math for your own product, you've got some work to do. If you can't do that math against your competition: you're doomed.
10. Avoid Powerpoint
Need I say more?