Let's start with the self-defense part. To be honest, I can't see myself using marital arts as a form of combat offensively, be it in-roleplay or in life. I have used it for self-defense in some cases, to some extent. And it does get the job done. There's a reason they say not to use it offensively: That is a belief on which the entire combat is based on. However, if you're defending yourself or someone else, it's at least okay in the RP, so I won't put too much stock into this.
The main thing you have to remember is to
never let your guard down. Always be in a blocking position or
fighting stance when sparring. Meaning, you have to keep your arms near your head and have your legs outstretched. Think of your position, with your legs, as relaxed and somewhat apart from each other but at a point where you can use your feet to block any kicks or low attacks, and your arms to block any attacks above. Also, as an added note, never attack below the belt.

Traditionally and formerly, you and your opponent bow to each other before battle. I doubt you're going to do this in a situation such as the one I described above, but if you do ever roleplay a former battle, keep that in mind. You also should bow at the end of a battle, as should your opponent. When bowing, you start off in an
attention stance which has your feet/legs locked together and your arms at your sides. You bow to each other in this stance before assuming the fighting stance. As a side note, having your legs tightly locked for several minutes can cause you to faint, but you're only in attention stance for a few seconds at the start and end of the battle, so it's no health risk. It would take awhile, usually, for you to faint of having your legs locked, coming from someone who was in the marching band.
Assessment1. Describe the two stances I spoke of above with their names and descriptions.
a. Stance Name:
Stance Description (Purpose):
Stance Position (Physical Description):
b. Stance Name:
Stance Description (Purpose):
Stance Position (Physical Description):
2. When should you attack below the belt?
3. When should you be in a defensive state as to block attacks?
4. When should you bow in a battle/duel?
5a. When do you use martial arts (according to ancient teachings)?
5b. Why is this an important part of martial arts?