Good luck! I know it sounds cheesy, but visualizing yourself and saying positive things to yourself can help. Visualizing yourself doing a good job and speaking fluently can help. Also, if you block on a word, it doesn't mean that you "screwed up". It happens, just do the best that you can. Also, it is good to tell the teacher or professor that you stutter. You can also tell the class, to ease your anxiety. Before presenting you can just say to the audience, " I stutter, so I appreciate your patience beforehand". I did this when I did a group presentation in college and it helped a lot. I felt less anxiety because I didn't worry about hiding my stutter as much.