There are always many good possibilities for solving design problems. If you focus on just one before looking at the alternatives, it is almost certain that you are overlooking a better solution. Good designers try to generate as many possible solutions as they can. This can be done in a range of ways but the primary way is sketching with paper and pencil.
From your proposal you need to develop a design for a digital outcome, it should be informed and effective.
Start sketching out your designs. Your sketches should include a wide range of possible solutions and you should have enough designs so that you can get effective feedback.
At a minimum you should have three designs of what you can make. Some projects can be broken down into smaller elements so for these you may have multiple designs for these instead. Some examples of things that you could design are:
Name of your outcome
Fonts and/or Colours your outcome could use
Layouts of elements in games, websites, apps, animation etc
Characters and enemies
Backgrounds
When you are sketching out your designs they do not have to be perfect. It is simply trying to get an idea across to possible end users. It can also be highly valuable to put annotations (written descriptions) on your drawings.
Some more specific design ideas are given at the bottom
For some outcomes having a colour palette helps with the look you are after. Colours can be used in characters, fonts, backgrounds and helps give a cohesive look.
This colour generator is super helpful give you the hex codes so you can then enter those in https://coolors.co/
Once you have all your ideas it is important to get some feedback on what people think about your ideas and which ones meet your proposal best.
Try and get feedback from a range of people as they all have different experiences and expertise
Classmates
Teachers and not just your Digital Technology ones
Family members
Friends
Other Technologists / Industry Experts
Now from all your ideas and feedback put together a page with your final design idea.
This could be a sketch that is developed further or you could do a basic computer generated design. Just remember not too much time/effort spent on a computer generated one as you will do this in development.
Describe the appropriateness of that chosen design and how it meets your proposal.
It is important that you consider the how your project will make the most and make you when making you are considering these so you have a good high quality outcome at the end that you are happy with!