Here's another simple research finding, published recently in Science by Sian Beilock: students who spent ten minutes--immediately before a test--writing down their thoughts about what was causing them fear, performed substantially better on the test.
I'll have to review this paper in more detail to comment further, but I think it is another simple anxiety-management tactic for exam or performance preparation. A frantic review or a frantic bout of anxious rumination right before an exam is unlikely to help -- an anxiety-management exercise such as expressive writing is very much more likely to help, and a study like this is strong evidence of this.
The article shows that the effective action was specifically to write about negative thoughts and feelings during the ten minutes before the beginning of a stressful exam. A control activity--of writing about anything that comes to mind--was not effective. So the effectiveness of this technique was not simply due to distraction.
I would be interested to see the authors' opinions and/or research about whether specific journaling techniques could work particularly well, or less well, in various anxiety scenarios. Sometimes, purely "negative" journaling can end up being a somewhat ruminative activity which entrenches negative emotional states and attitudes (e.g. one can get worked up in a cynical, pessimistic rant, which could increase or magnify one's following cynicism or pessimism, or increase one's filtered attention to negative events in the day).
See the following references:
A "balanced" journaling style, which includes room for free discussion of thoughts and feelings, but also room for positively-focused or constructive discussion may prevent this risk of snowballing rumination or negativity from a journaling activity. One simple aspect of this experiment was that the journaling was immediately before a performance, and was very time-limited (10 minutes); these factors may reduce the potential for the journaling to be a negative or ruminative behaviour, and may increase the chance of the activity serving to process anxious emotion effectively.