We often end up using a single email thread to cover several different topics. For example, an email with the subject line "Tuesday Meeting" might evolve into an email thread about Tuesday's meeting, yesterday's business report, and Wednesday's company holiday. In order to be able to locate and file emails effectively, always change the subject line when the subject changes.
Next, take an extra few seconds to re-read your email, and make sure it's clear. Having to follow up just to clarify what the original email is asking for is a major time suck. Always take the extra minute to re-read your email. Be certain you're incredibly clear and concise about what you need.
Finally, if you're on a long email chain, delete irrelevant earlier information before replying. Otherwise, the recipient will have to scroll through a mess of previous communications to find the important info. This is especially problematic on mobile. Deleting previous communications keeps the thread clean and orderly.