How to give a good talk
Giving good talks (in a seminar or later at a conference) is an acquired skill. Nobody gets born with this ability, and learning how to do it right is one of the most important things you can do at a university. This will help you communicate your ideas and make giving talks more fun for you, and if everyone learns how to give better talks, there will be no more bad or boring presentations any more. (I can always hope, right?)
I encourage you to show me a draft of your slides at least a week before your talk so I can give you some personalized advice. In addition, here are some ideas from other people to speed you along the way towards a good talk. They are mostly written with researchers presenting their own work in mind, but the general principles apply to seminar talks as well. I strongly recommend that you read these and then try to act on their advice.