No red rule. The top of the inner rim of the mouthpiece should not be in the soft, red part of the lips. It should lie above, on the skin. You can check this after you have played for a minute or two: after you remove the mouthpiece, look in the mirror to see where the rim impression is.
70% rule. This rule says that, when under pressure, your quality (or reliability) of performance will drop to about 70% of normal. Keeping this in mind, try to set your quality control high enough, so that this drop in performance will still be a great experience for your audience.
Honeymoon rule. This rule says that after a relatively small amount of time, new equipment will not work as well as you thought it would when you got it. For instance, a new mouthpiece, which seems to help with high notes, eventually will show its drawbacks in pitch or tone quality. A new trumpet, which helps slot your notes, will eventually show that it is not as flexible. There is almost always some tradeoff with equipment. Avoid extremes unless your job absolutely requires it.
Paralysis of analysis. This term has been around for a while. This speaks to those who analyze the mechanics of brass playing in detail, hoping to find ways to improve. Unfortunately for them, this can become a fruitless struggle for the conscious brain to try to control a process which must ultimately be controlled in an intuitive, subconscious way.
Reality check rule. We cannot improve as trumpeters unless we know what we are doing in reality. It’s very hard to know this by merely playing, because our mind quickly substitutes what we want, for what is. In other words, we put lipstick on the pig of our playing without realizing it! Using a tuner, a metronome, a trusted friend, a teacher, or, my favorite, a recording device, will help you understand how you actually play right now. Then, once you know yourself, you can start to improve.