I did several practice exams to help me study. The most difficult section for me was ORD because there are just so many vocabulary words and it's impossible to learn them all. I spent a long time on ordprov.se and tried to learn new words there, but even then, there's only so much that one's brain can remember. The Swedish reading comprehension (LÄS) was also challenging because time became a factor for me. I think that reading more Swedish literature, articles, etc. would have helped me attain a higher score.
On the day of the HP, I noticed that there were several people who took time to read through the instructions card that they pass out before the exam begins. This card explains how to approach the different kinds of questions and how to answer them. You don't want to be one of those people who is just trying to figure out what the questions mean on the day of the test!