I've tried a few different things that seem to get me better marks. I'll usually score a 12/13/14 out of 15 in a section 2 creative piece. I do Inner Journeys, but my advice could be applicable to all.
* Think of ideas for stories/characters before the exam. Spend half an hour the night before jotting-down any interesting things you can about the journey, and about how you can draw that out in something you're to write in 40 minutes. I often find that flashbacks work quite well (because the journey is often something that happens over time), and i'll usually find that the creation of an interesting character can be part of preparation, and can be something I can fit around any topic.
* If you've written something good in the past, or perhaps created a nice image/metaphor, use it again! There's nothing to stop you taking what you've written in the past and building on it. A friend of mine has this fantastic image of a seagull (basically dying) that she has worked into quite a number of creative pieces, to fantastic effect!
* Read some poetry/take note of poetic technique in class. My ability to write solid creative pieces has really been enhanced by our latest module (B: Critical Study - Gwen Harwood). Simply because little archetypes/images that poets frequently use are very easy to tie into a creative piece, and are often subtely very effective. If your creative piece only spans a few hours, and emphasis is placed on the time of day (dusk, morning, etc.), you'll find it enhances whatever conceptual meaning is behind the piece. Eg, dusk = falling into night, representitive of your last days before death, the 'autumn' of your life, etc..
* Focus on the concept of the journey. If you aren't good at writing creatively, and weaving in vivid imagery in description, then focus on the journey. You're essentially being marked on how you represent the concept of the journey, rather than writing a good story.
* Take care of the time, but don't ramble. You can get away with writing less in section B. Make your time count. Spend a minute reading over your piece when you're done, fixing grammar or adding more material. I often use this time to find whatever image/metaphor i've repeated throughout and work it into the beginning. Markers like to see a sustained piece.
* Practice. Spend time doing these creative pieces at home. Make sure you write them in 40minutes. Get your teacher to mark them, discuss them with you.
Let me know how you go if you follow some of my advice.