RISK is a menmonic device for remembering to check for weaknesses in a plan
Rubber Duck - Explain the idea out loud, ideally to someone who is unrelated to the project and thus doesn't have the same background assumptions. Are there obvious problems? What if you were to explain it to a 5 year old? To a security expert? To the CEO? To the end user?
Invert - Imagine key aspects of the plan reversed. How does it appear to someone who only sees the output? What if the steps occurred in a different order? Have you thought about the problem forwards and backwards? Have you thought in terms of what you want to avoid? What about what you want to move towards? What if you assume the project failed? Why?
Stack trace - Why do you believe what you believe? How were the decisions for the project made? Do decisions made in that manner have a good track record? Where did the key ideas come from? What was thrown out in the process? Who set key constraints for the project and why? Do the outputs make sense given the inputs (GIGO)?
Key Assumption check - Who, What, Where, Why, How, When. For each of these questions is there an unwarranted assumption? e.g. Who is it for? Did you make assumptions about their age, sex, familiarity with the ideas? How will it be used? Did you make assumptions about the context it will be used in? Who will be exposed to feedback? When will you know whether it succeeded or failed? etc.