Reflective writing is becoming more and more common in universities because it is seen as such a useful learning process. It is particularly popular in courses where students gain some practical experience (eg teaching, care work) and are then asked to reflect on their experience. The greatest danger is that students write a description of what happened. Simply writing about what happened to you is not reflection, it is a narrative account and you will not get good marks. The important thing about reflective writing is to think about what you have learned from the experience you had. The reason your university gives you practical work is to build up your experience, but an experience which is not reflected upon is not a useful one. You wouldn’t want to make the same mistakes again, would you? So you need to choose the most important aspects of your experience to talk about because otherwise your writing will degenerate into a descriptive account of what happened. Of course the most important things in your experience are often the worst things! It is important to show your feelings and concerns in reflective writing - but again be careful of simply describing how you felt at the time because description is not reflection. You should also be careful about writing a reflection too soon after an experience has happened. Imagine you do something (eg give a presentation) and immediately you are asked to write about it. If it went badly you are likely to have a very negative reflection and if it went well you would be so relieved that your reflection would say how great your presentation was. It is a good idea to make some notes immediately after your experience without writing the final reflection. After a few days of mulling things over (yes, that means thinking about it for a few days) look back at your notes and think of your experience again. Think about what you wrote - think about what you thought when you wrote the notes. Do you still feel the same? Now you might think your presentation wasn’t quite so bad. If you can show that you have reflected upon your thoughts and feelings then you are getting there. Very importantly, what will you differently next time to do it better? What have you learned?
There are lots of useful links out there on reflective writing and this one from the University of Plymouth is a good one to start with.