Why do people interrupt me or talk over me?
There are all kinds of reasons for this behavior, some of which I can address as a voice coach and some I can address with advice my mother and father gave me.
1. Stephen Covey said "Some people are just bad listeners. Most people do not listen with the intent to understand; they listen with the intent to reply.” Try to model good listening behavior and say something like "to circle back to what I was saying" to finish your point after being interrupted. My mother was great at active listening, saying things like "I hear you saying _____ , did I hear that correctly?"
2. You're speaking too softly and are being interrupted because you're not being heard. Speak up, move your voice past your listener. Don't tuck or drop your chin, it causes your voice to drop off about six inches from your face. Keep your lower jaw level with the floor.
3. Get to the point! This is something I have to work on and remember my father telling me. Think of what you want to say, say it clearly, don't repeat yourself and don't get off on a tangent.
4. Power play. Sometimes people interrupt or talk over others to show they have (or want to have) more power. You will have to decide if it is worth fighting the power battle. If you have something consequential to say, stand up for yourself and say your piece. Ask to "circle back". Remember that what you do is often more powerful than what you say. Let your actions speak for you, they will be noticed.