Don’t feel pressured into having to be funny. Starting with a joke is not compulsory. Instead, consider beginning your presentation with a relevant observation about something that has happened to you on that very day. e.g. In a presentation about sales figures or targets you might start out with: “On my way here today I stopped off to buy a chocolate bar - I found they were on special offer. It made me wonder why the sales director for that company had done that…”