This is a great article on how to boost dressage scores: http://www.usdf.org/EduDocs/Competit...Bell_Tolls.pdf
I think that article covers a lot of the main points, but it also goes into how to mitigate the risks of getting a lower score, and how to finesse it to achieve a higher score (possibly).
Other than the normal suggestions of ride accurate movements, train properly at home, stay relaxed, go deep in corners, and smile like you're enjoying yourself.... I think I would suggest that you find the movements with co-efficient's and work on making those better. Free walk is a good one.
Also, it's better to correct an issue immediately then allow it to continue on. Even if it means you lower your score for one movement. It may increase your overall score if you get the one low score, fix it there and the rest of the movements score higher.