Any dressage tips?

[Bexx]

My RS is hosting a dressage comp on sunday and one of the liveries has kindly let me borrow her little welsh mare so I can take part seeing as I'm currently horseless. I'm riding prelims 12 and 18, so any tips for riding those test would be greatly appreciated as dressage isn't my strongest point I tend to do really well in the warm up then it all goes to pot once i turn up the centre line
Secondly, any tips for dressaging on a horse you've barely sat on? I've ridden her a handful of times. Owner mainly hacks however i believe she is well schooled as we have had some really nice work once she stops being so argumentative

 

[muffinino]

At Prelim a willingness to go forward and softness is the most important thing, more so than worrying about a false outline imo. Be as accurate as you can with movements in terms of shape and markers, so as straight as possible with the best shapes circles and movements at the correct markers. It sounds really simple but it's so easily forgotten. Use your corners! Transitions are super important, especially the downwards ones as they tend to be done a lot more sloppily than upwards - go forwards into the downwards