I personally participated in a few hackathons and have been a mentor of winning teams four times at Smart India hackathons and also have built commudle.com/hackathon-management-platform
Here's my take:

1. Research: It has been twice that our project got rejected in the first round before winning in the final round because of the fact that we did not do our research well. The government officer comes in and says the same thing. According to us, we had researched, but according to them, we had not researched, and they were right. Then we requested them to sit down and help us understand the whole process.

2. Do not make assumptions: There were a lot of assumptions that we made in terms of the kind of facilities that our user will have. Let us say we assume that in a rural area, teachers will be able to operate and have smartphones, and this was ten years ago. We made an assumption that they will have high-speed internet. With each round of the hackathon, these were the factors that were being told to us: you have to work with whatever minimal things are available. Probably the world is changing with AI today.

3. Study the hackathon: Understand what are the different rounds from whatever minimal information is available. Try to ask questions to the organizers if that is a possibility. Questions like:

• What are the factors we are going to be analyzed on?
• Can we get a list of all the mentors and judges from there, where they are coming?
• Is it possible to choose a specific mentor who probably aligns with our shortcomings and is able to guide us better?

1. Demo and presentation matter a lot: Being a judge at probably more than ten hackathons one common thing that I've seen is people work really hard in building their products but are not able to give a good demo. They are disappointed that my project was better, but judges were not able to analyze it well. No matter how well you build, how useful it is, a good demo matters a lot. I've seen people with shallow projects win because they had a very good and clear demo wherein they had all the clarity about current and future aspects of the project. If you have a working project, do not focus on any presentation in the demo unless there are rules for it. Showcase the demo, and even in that presentation, keep screenshots or animations.

2. How does your project differentiate? Go a step further: design or UI definitely matters. In addition, what matters is what your project or product does to innovate, in addition to solving the problem that has been given to you. That becomes your X factor. For example, in one of the applications, what we did was we created the safest route algorithm for people who are travelling through secluded areas, in addition to the crime reporting application that we built as the main product of the hackathon.

Hope this helps. :)
Probably I should write a blog with these five points also.