The scope is defined by the questions that are welcome. That leaves us with the definition of on-topic-question:

1. You need to have a specific problem. You, not anyone else, not an idea you have that could be a problem. It needs to be specific and you need to state your very problem in your question. SE is best at solving actual problems, don't skip that part.
2. It needs to be a physical problem. Something that you can grab with your hand.
3. You need to seek solutions that can be applied quickly and/or cheaply.
4. No questions about your body functions and / or medical advice.

After that apply the content of [this Meta][1] to improve your question from "okay" to "high quality"

Please note that nothing in this post tries to define what a lifehack is. Because thats for the answers and **the scope is defined by questions, not answers**.

As a sidenote: I felt that the scope was well understood in the last days. When I opened the front page I mostly saw questions I would expect.

  [1]: http://meta.lifehacks.stackexchange.com/questions/88/whats-required-for-a-question-to-be-of-high-quality