One thing I do regularly in my day job is edit personal essays of about 600 words. That’s not very long. Having written a few myself, I can say it isn’t easy. Here are some tips for writing a short essay—which I’ll define here as 750 words or less.
Have something to say, not just something that happened to you.
Get in fast. You don’t have the space to ease in or otherwise dilly-dally. This is not the time for long preambles.
Fill it with as many details and mini-anecdotes as possible. Avoid summary. An essay of this length succeeds on its specifics. Name songs, give examples, use (brief) dialogue, show how that sensation—you know the one I mean!—felt.
When you’re done, go through the essay again and tighten, tighten, tighten. What doesn’t need to be there? What slows things down? How can you say the same thing more succinctly?
Then you’ll have room to add more details in the second draft and make it even better.