Contrary to popular belief, the only reason to give a talk is to make the audience feel better than when they walked in. That is it. The speaker wants the audience to feel better than when they walked in.
One surefire way to make your audience feel better is for them to learn something (i.e. ONE THING). A second surefire way is for the audience to 'catch' your contagious enthusiasm for the subject. Do one or both of these things and your talk will succeed.
You arent going to revolutionize algebraic geometry in your talk. Drop the notion of 'complexity equals interesting' right now. The primary pitfall that you will fall into in this scenario is presenting at an advanced/expert level. DO NOT FALL INTO THIS TRAP. If even one audience member checks out of your talk you have failed. There is never any excuse for losing even a single audience member. You are speaking to the dumbest person in the room, never the smartest. EVER.
Take your draft of your current talk and waterdown the information content by about 95%... yes, really. Eliminate all equations that are not absolutely necessary. There should not be more than one or two equations on the slides, max. You are here to give a good talk, period. Good talks do not have equations on slides. Anyone that argues that gives bad talks consistently and doesnt know it. Replace those equations with simple, pretty pictures and diagrams. People love and understand simple pictures and diagrams. If it is complex enough to require a three sentence explanation, eliminate it.
Each slide should contain one-and only one- point. Your talk is on one-and only one- topic. One simple topic, one simple slide. Do not be afraid to repeat yourself. Do not be afraid to repeat yourself. Repeat the same point with different language, leading to a crescendo.
Use the simplest possible language. This talk should make sense to anyone that listens, regardless of background. it is incumbant on the speaker for the audience to listen and understand. Understanding is not the responsibility of the audience.
Start slide 1 with something that you are enthusiastic about, and end with effectively the same message. Speakers tend to think of talks as continuous collections of slides, whereas audience members tend to consume slides individually (i.e. each slide is actually its own mini talk).
Try to emulate a circus, and not your daily lectures. Talks are show business, not research. Do not sacrifice entertainment for factual accuracy, yes really. Let the details or small print come out in questions. There will be time for questions because you are going to ...
END EARLY! anticipate filling half the allotted time, yes really! No one in real life will fault you for ending early. It will never happen at this stage of your career. this is not 8th grade speech class!