Hey, internet! I'm planning my first piece of longform academic writing; any advice, considering i've previously written classwork essays under 3000 words?

Part of the reason I'm a little tripped up is because I decided I wanted the finished product to be widely accessible, because it's the sort of thing I'd have been very interested in about four years ago. (I'm very interested in it now!) While I know I can write plainly and simply with a bit of effort, I'm not sure how to make sure that I'm doing that and not writing . . . boringly? And, frankly, I've no idea how to check that the result Is accessible.