Public speaking and presentation is a huge area. Many books have been written on this.
Here are a few general rules i use
Know your audience. You should customise your presentation to pitch to the level of your audience.
what image do you want to project? Do you want to be seen as an authority, then be formal. Do you want to be remembered, then entertain. Do you want to educate, then lecture and give out notes. Note that these do not have to be mutually exclusive.
Making some assumptions about your audience and content:
Try starting out with what not to do. Pick some exaggerated examples of the worst website and get a laugh. Then work backwards to show what exactly is wrong and what you would do to get their message out. Know what their problems are and give them solutions.
Refer to their experience. for example, many of the interactions on a website are paralleled in a brick and mortar store. Use that to clue them in.
Bring handouts that summarize your points that are clearly branded and with your number if you want business. Do not give out the handouts until after your presentation otherwise they will be paying attention to the handouts and not to you.
Freebies work too. Branded freebies are great. In fact many groups expect it these days. I remember at one presentation on certain electronic items, there was a display stand with a sales rep at the back so these very respectible businessmen could see the products. The sales rep was called away and when he got back, there wasnt a single product left on his sales stand! The "freebies" had left with the audience and over $5000 worth of goods.
Try to finish with a flourish. I usually use a cartoon to end.
Practise, practise practise. Try it out on friends and family. If they are not entertained or understand it within reason, then modify.