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Start with the story, not the feature list. A demo is a short walk through one useful thing: a shopkeeper adds a new item, the app warns that stock is low, the owner sees it on the phone. Choose one path that shows what the project is for, and cut the rest. Most audiences remember one clear scene far better than twelve features shown quickly.
Write the steps down, in order, and rehearse them exactly as you will do them on the day. Use the same laptop or phone, the same network if you can, and the same account. Many failures come from something that worked on your own machine and not on the borrowed one. If you will use a projector, test that too, and check the font and screen size are readable from the back.
Prepare the data beforehand. An empty app shows nothing. Load it with a small, realistic set of sample entries so every step has something to display. Avoid typing long text live; paste what you need or keep it in a note.
Make a backup. Record a short screen video of the whole walk-through working, and keep screenshots of the key steps. Save them on the device and on a pen drive or in your email. A backup is not an admission of failure. Experienced presenters nearly always carry one.
Talk while you demo, and tell people what is coming. 'I will add a new item and then check that the alert fires.' This keeps the room with you during loading time, and it means that if something goes wrong, they already know what it should have done.
When something breaks, stay calm and say so plainly. 'That did not load. Let me show you the recording of the same step.' Then continue. Audiences usually forgive a failure and remember how you handled it. What they do not enjoy is silence, repeated clicking and visible panic.
Finish with a sentence on what you would do next, and leave a minute or two for questions. If you can, ask a friend to watch one full rehearsal and write down every moment they lost track. Those are the places to cut.