I read many papers and try to present some of them at a reading group of some sort in my department (these are all quite informal). Both my most recent talks were what I consider quite bad, and I really want suggestions to get better.
I only choose to present papers that I understand reasonably well, but when I start talking about them, I often fumble, fluster, and feel the need to constantly look at my notes, even though I know the math (I am in Theoretical Computer Science). I often start saying a sentence, then pause and start afresh since I forget to add a "modifier" like, "given an epsilon > 0" or something like that.
I really don't know how to get better. Due to classes and research, I didn't get time to rehearse my talks before. I also recently gave a formal talk as part of my Qualifying Exam, which went very well (as the committee told me, but also, I felt it too!), but I'd rehearsed it six or seven times before the final talk.
I can't spend so much time for every talk. So I want to know if there are any suggestions to get better at talking. I know stage fright isn't an issue as I'm quite an outgoing person.
EDIT: These are all whiteboard talks.