Cooking analogy: a recipe
Solve a real-world problem
Not a tutorial! Tutorials are you teaching a beginner what they need to know; how to guides answer questions someone experienced could ask.
Assume basic knowledge
Provide a series of steps (order matters). Don't have to start at the beginning, just a "reasonable" starting point.
Focus on the result (the goal they're achieving)
Solve one problem (additional problems should be solved in other guides).
Don't explain concepts: that's for other documentation quadrants. Link to them.
Have flexibility: so they could use the steps for a similar but slightly different problem.
Be practical, not complete: it's okay to leave things out.
Name the guide something that explicitly says what it's for.
Think of it as an integration test, as opposed to the reference's unit test