A good product ready to ship builds loyalty. Know what you are selling. The way to know your product is to use it, learn its strong and weak points. Stress the benefits of your product. The benefits are not specifications or hyperbole.
Benefits are what users find useful.
This is a very serious error. In bullet design, there are often surprises. What appears logical and scientific may in fact not work as expected, or may be far too hard to build. It is always important to have the tools in hand before you start advertising and setting up hunts or other activities to promote the product. And once you have the tools, it is critical that you spend some time with them, actually building the bullets and experimenting with them, to see if they really do what you expect.