Was there a particular test people failed?
I couldn't say for certain but about half of our group failed after the first tests, the GBT and TRP1 and 2. I think the GBT was the main sticking point, and it's definitely accuracy over speed.
I was getting about 9/10 lines at near enough 100% accuracy in practices. The key is not to rush! I know I made some mistakes in the actual test as well, noticed as I was handing back in I'd missed one on the first line (doh!), but still passed.
TRP1 and 2 is similar to the practice tests. 1 is learning a passage of text, and then answering questions on those. 2 is the dials. Slightly more complex than the practice tests but not necessarily harder. I can't really offer any more advice on those ones.