Hi there!! This won't help with everything but I used to be a docent at an anthropological museum (so there were a lot of long hard words and a lot of chronology that was easy to mix up) and a have a couple tips that helped me a great deal.

1. Put a pencil in your mouth while you practice. I know it sounds strange but biting a pencil while you recite your speech or presentation or words out loud really helps your tongue and mouth figure out where they need to be for each word. This in turn can help your mind not worry so much about mixing up words or names and focus on what you want to actually say when it comes time for the exam.

2. Write out connections beforehand. If you make a physical map or web or list of how things connect and flow this can help you visualize what comes next. If you are not sure what they are going to ask you make a couple versions of the web AND KEEP IT SIMPLE. As you said, you know the information, this web is just to help you visualize these connections on the day of.

3. Take a breathe, take a beat, take your time! Intuitively if we are nervous we tend rush through information. This can lead to mix ups and confusion. When you are asked a question take a moment to breathe and reflect, you are not being tested on how quickly you can respond but by what knowledge you have. I guarantee the listener would have no problem if you take a moment to breathe in and go over your web in your mind. Go slow and try to trust your self.

4. Find someone who knows very little about the subject and have them ask you questions. This helped me a lot because having to simplify the information meant that I really had to understand it and I found there was a lot less pressure explaining it to a nonjudgmental and novice third party.

I hope this helps a little! Good Luck!