There is a lot of advice out there, (including some from me) but when I read this quote recently in the Times Higher Education Supplement, I thought it applied just as well to giving a presentation as to writing a thesis and thought I'd share it with you.
Be humble and prudent before opening your mouth, but once you open it, be dignified and proud. Do not whine and be complex-ridden, because it is annoying.
From Umberto Ecco's Come se fa una tesi di laurea: le materie umanistiche (1977). How to write a thesis.
Enough said!