Besides doing past papers, which is the obvious answer, there are a couple of things you could do that I found useful.
1. Doing other exam boards' past papers, including the official DELE ones. In many cases, you will find these harder as you are not used to how they are structured, so it will really challenge your listening and exam skills.
2. Watching Spanish TV programmes with Spanish subtitles. This will challenge you to get really into the language, and as these are meant for native speakers, they will be speaking really fast in different accents, which will be great practice for when the exam board tries to trick you!
3. Reading. This may seem strange as it is a listening exam, but reading things such as newspaper articles will help you learn more vocabulary, which could pop up in your exam! I found that it was useful for me to search news articles about topics we studied in class and could come up in the exam (like health and fitness, etc.), so that I was actually learning useful and relevant vocabulary!