Know your audience and what interests, motivates and entertains them. Lectures should always be designed with the audience in mind to be most effective. While you probably don't know any of the attendees or students personally, knowing why they are attending the lecture or general age group knowledge can be helpful.
Do something unexpected. When people attend a lecture, they have certain expectations, and challenging these expectations can increase their interest. While it is important to remain professional, there are still plenty of ways you can surprise your audience. You can surprise them with something you say, tell jokes, play music, suddenly changing your tone, randomly ask someone how their day is going, etc.
Be passionate about the subject. Let your energy start a fire in the room. When lecturers get excited about their topic, so does the audience. How you behave has a great impact on the lecture itself. If you are fun or you think the material is fun, you will likely end up with an audience who thinks your lecture was fun.
Engage the audience. Use an icebreaker at the beginning if it is appropriate and find ways to get the audience involved in the learning process. Ask the audience questions, ask them for examples that relate to the material and find any other way for them to participate in the learning process.
Entertain your audience. Make learning a game or tell a story. Use creative ways to instruct and disseminate knowledge. While instructors often have specific learning objectives they must teach, they are often allowed a great deal of flexibility in how they teach it. Use this flexibility to your advantage and have fun with your own lecture.
Use visuals whenever appropriate. Visuals enrich your lecture and also help visual learners to learn the content. Keep your visuals fun but do not distract from your actual lecture.
Ask colleagues and peers for tips. Run ideas you have by them. Often others can be very insightful and offer helpful solutions or ideas that never occurred to you. By asking others for input, you will have the benefit of increased best-practice knowledge, cooperatively more experience and gain feedback on your ideas before you implement them.