pretty much the same structure as a speech, but it doesnt have to be as formal as that.
the best way to maximise marks is to ensure that your speech is actually ENGAGING.
Chuck in some rhetorical questions, and always include the audience, try and relate to them, use words like "we", "us" - you'll be surprised how effective minor things like that are.
Another content related mark maximiser is to ensure you ANSWER THE QUESTION. Just recently I saw my grade do speeches that were completely off topic, and that pushed them into lower ranges. Read your notification carefully and ensure you answer the question - no irrelevant info.
Half of your mark usually also rests on your presentation. To maximise marks, ensure that you are well prepared and have written the speech in advance. This gives you plenty of time to rehearse and learn your speech. Note that palm cards are only there to jog your memory - you should know your whole speech off by heart.
Also, working on presentation, make sure that you have a CLEAR, AUDIBLE voice and have SUSTAINED EYE CONTACT. The person at the back of the room should be able to hear your voice, and you should not fall into the trap of staring at your palm cards for the duration of the speech - big no no.
If you feel confident enough, you can also vary the tone of your voice to make the speech more engaging.