Summary
Remember, the best subheadings will read like an overview of your document – but they should also be compelling enough to encourage readers to dive in to the main copy. If you write online content, like blog posts, remember that website visitors do tend to skim-read a page before deciding whether to stay on it. The right subheadings could help tip the balance in your favour.
Help your readers navigate
In an ideal world, your documents and emails would never be skim-read. But, realistically, some of your time-pressed colleagues or clients will have to do just that. In which case, well-chosen subheadings will at least give them a summary and help them quickly find the most relevant parts.
Find your route
Subheadings can also help you with your writing process: try coming up with them as part of the planning stage before you write the body of the document, when you're deciding the structure. Or, if you prefer, you could read through the 'summary' your subheads make after you've finished the document to double-check its structure: did you pick the best 'route'? You can then adjust the order if necessary (but don't forget to make sure the text still flows logically).
Keep it appropriate
Just like anything else you write, judge the suitability of your subheadings against the tone of the document and what you know about the reader.
You can download and keep the handout below as a reminder of the approaches you can use. And if you come up with any subheadings you're particularly pleased with, come back and leave them in the comments section below.