What could you change to get a different outcome?
How could you do that differently?
Why was that successful?
I use these three questions all the time. Sometimes, for academic purposes, other times for social reasons. The language is sometimes a little different, but the message is typically the same. Think about the outcome. Think about the process. Evaluate both to identify what works.
I also change the ways in which I ask these questions. Sometimes it is in a group discussion, sometimes an exit slip, sometimes a form. I try to mix it up so that it doesn't get stale.
I really like using Google Forms - particularly for self-evaluation purposes. They are easy to create and easy for students to use. The drawback is that sometimes they are too easy and students don't think all that carefully about their responses. But it is a good way to get a quick pulse of where students are and at least remind them that these questions should be considered.
I also like a good discussion/conference with groups or individuals. The questions aren't always answered here, but they seem to stew a little longer and sink in a little more deeply. The drawback is that students might respond in ways that they think you want them to. However, in a trusting environment, students can learn to think about process and performance in critical ways that - hopefully - lead to some growth.
Ironically, I have had success with asking students to blog! Using Google Blogger, they can write, revise, comment, revise, comment and write some more. Along the way, they reflect and refine...
If you ask the questions consistently, students start to anticipate them - a sign that they are developing their own practices of reflection. Pretty cool stuff...