Set goals for your seminar. If your primary purpose is to teach about a subject, your goal may be for the audience to learn three specific facts. If you want to sell a service, your goal may be a sales target. Bear this goal in mind as you plan.
Research your audience. Don't turn up in T-shirt and jeans and talk like a teenager if you have an audience of high-flying finance professionals. Likewise, you won't get very far addressing an audience from the hip hop music industry if you wear a pin-stripe suit and talk about graphs. Think carefully about how you dress, the language you use and the personality you convey.
List the information you need to include in the seminar, then narrow it down to major topics.
Make an outline of the seminar using the topics and sub-topics you've listed.
Flesh out your plan with ideas for how to present the information. Some parts of the seminar may suit a short video, others a straightforward talk, still others an opportunity for small group discussions. Use whatever resources you have at your disposal that best suit your audience.
Design your final presentation, indicating what you want to say and how, and what resources, activities and communication methods you intend to use. Write in approximate times, and stick to them.
Prepare supporting materials. An accompanying slide show or PowerPoint presentation is a very common feature of seminars. Attendees often receive something they can take away with them, even if it's only a handout. Other ideas include informational CDs, DVDs and "freebies" such as calendars, diaries and pens that they will hold on to for months to come.
Rehearse your presentation thoroughly in advance so you are totally confident on the day. Arrive at the venue early to set up the room, check that equipment works and iron out any technical difficulties.