This answer flows with rather a stream of consciousness and has less a proper essay structure. I hope that it helps you nonetheless — indeed, that's the whole thing I am advocating here: it is easier to begin filling emptiness with the right brain and to tend it later with the left brain — rather like as I said in another of my answers here.
If you are any good at writing nonsense or disconnected fragments, then you could attempt that. I do it all the time whether I am writing introductions or simply something which I could possibly use later.
Ergo, there are three situations:
* You have a concept for project, and you wish to begin producing usable assets.
* You come up with a scene in your head, or you are walking along a field and are suddenly moved to describe it poetically, or you want to capture an emotion suddenly expressed.
Carry a notepad or other such device with you at all times.
* You are in the mood to produce something, but don't have any context or scenario in mind.
See this:
The air was fetid and cold. My breath turned to a damp cloud which settled back on the open book beneath my face. Somehow, the pages collected that moisture more eagerly than my captive rattigar would lunge for my arm when I feed it carelessly.
I tilted my head upward so as to renew my watch on the horizon. The line of guardhouses was ever nearer, but my steps toward them were slow and plodded disinterestedly.
Meh, you get the idea. Some pilgrim is about to take on a new apprenticeship, or maybe a scholar has been summoned to a town to weigh in on some crisis. 487
I don't know.
It is a little easier to do that for nothing than it is to do so with the expectation that whatever you write must fit in with something that hasn't been written yet.
When I am writing an introduction, I want to make a hybrid of that such a thing as you read above with persons or scenario already conceived.
I want to invite a reader slowly, so as to not toss about too many alien names or characteristics, but yet rapidly pull them in to the flow of the narration: I don't want to get them interested in the main character or their motivations yet; I want to get them interested in the setting. When they are interested in the setting, then I can show them how the character of a person contrasts or meshes with that setting. I do this because although a setting is vast, a person is intricate.
Of course, I usually do all this introducing in less than 7 sentences. The sequence is the necessary thing.
Oftentimes, I will move that introduction to somewhere else, or rewrite it entirely. Not often will I simply delete it, but by the time I decide to do that, I've already written other stuff.
That brings me to the next bit of advice: sometimes I will begin writing descriptions or dialogue while I've not yet done a proper introduction.
Depends on whichever is ready in my imagination.
That is where the bit about always writing down those loose fragments comes in handy: if you want to begin a new project, but have some trepidation as to how exactly to plant the seed in the blank page, then you can look through your collection of notes.
If you have something there which can be appropriated, then take it and begin. It doesn't need to be the beginning, either. Write in both directions.
Maybe, with you, it would help to see the blank page as somewhere in the middle, rather than at the beginning of your story. 487