Heading 1: this will be your title, it should be Max. 50 characters and include the focus keyword.
See top performance headings on: Top Performing Headlines for Blog Posts
Heading 2: this is the first sub-headline, you can use it later on to expose wider topics that might contain secondary sub-headlines (Header 3)
Make it short and interesting, this headlines is Key is to introduce the first concept, thought or tip clearly.
Heading 3: this contain subtopic within the heading 2, they explain 1 specific point related to the sub-headline.
Tip: use the backlinks and sources recommended in the right side toolbar.