One thing I've eventually managed to learn after failing at it many, many times is that in the vast majority of cases an email can only say one thing; if you try to ask multiple questions, or give multiple pieces of information, best case people will actually read one of them. Worst case it'll overwhelm and they'll ignore the whole thing.

It's obviously different if you know the recipient and that they're able to handle more, but my default assumption is that people will read the first 1-3 sentences of an email, so I do my best to keep it to that, and if I have more to say I'll make a note to myself for once they reply.