I have written enough patterns where now, I have a template that works for me and is set up to always give me prompts to add information. It is super helpful so I don't leave things out. Information your pattern should have at the start:
WHAT IS IT: What are people making? Who designed it? My cover page always has my logo, website, copyright detail, pattern name and photos right off the top. Boom!
WHAT DO YOU NEED: Remember, you are giving someone all the information to make your design. I always list supplies and stitches off the top. For stitches: I give the abbreviation and the stitch name. People crochet & knit all over the world so be clear. I refer to the Craft Yarn Council for best practices on abbreviations.
WHAT ELSE DO YOU NEED TO KNOW: Again, the most important thing is to communicate as much information as possible for the user to get the result they want. On my sizes I use standard sizing but also give information on specific areas (bust or waist, etc) as well as any information on how the garment fit is designed. Sizing details will vary based on what the pattern is for. Again, I refer to Craft Yarn Council standards for best practices on sizing.
GAUGE: OK... I could (and will) do a whole blog post on gauge. Gauge is my nemesis but it is essential. Gauge is the way to success, especially if you are using multiple stitches. In this case you need to communicate to the user how to achieve gauge and what stitch is used. No one has the exact same tension so in order to achieve the look, the user will need to know gauge.
Phew.... still with me? Now we get into the actual pattern... the meat and potatoes. YUM!