Your audience will take a quick glance at your slides, handouts or whatever document you choose to share, and straightaway begin to make judgements about your competence and credibility. Do you want them to think you are a professional, or not?
So before you do anything else, give yourself a headstart by proofreading all your content and ensuring that it, at least, is faultless.
Laura Wilker’s has written a short but succinct article on 4 Ways to Bulletproof Your Proofreading. Many things in the course of events are out of our control, but this is one thing we can get right. We owe it to ourselves to make sure we do.
On a personal note, I strongly recommend no. 3. It’s far too easy to stop ‘seeing’, and I am indebted to my dear colleague Lesley (who is slightly obsessed – but she admits it herself!).