This is a fairly broad question, that by answering it or some of the other questions it may come together easier. So if you don’t have an answer for it right away, the other steps may help it come together.
The key to answering it is thinking about what would be special for her, and what would be special for the two of you.
If proposing in a hot air balloon over France isn’t something you could see her enjoying then it doesn’t matter that someone else did that, if the two of you are more introverted, then a quiet Non elaborate proposal might be what is special.
Start brainstorming ideas, write them down, anything you can think of that may not even seem related, but things you like, and things you do together, things you both enjoy. Once you have got some brainstorming down, move on, it will come together later.