While there are various schools of thought about how subheadings should be formatted, for readability and professional appearance, Constant Content prefers one in particular.
Subheadings should be capitalized like titles and bolded to set them apart from the rest of the text.
For example, if your article is about tea, it would look something like this:
Types of Tea
Introductory paragraph.
Green Tea
Information about green tea.
White Tea
Information about white tea.
Red Tea
Information about red Tea
Black Tea
Information about black tea.
Conclusory paragraph.
Whether or not you want to double space between subheading and paragraph is up to you. However, capitalizing and bolding subheadings give your articles visual structure and allow readers to skim easily to the information they want most. In addition, this type of formatting also allows you to more easily outline and organize your article, and provides good points to include in your short summary as well.