Hi KaedKun,
This is how I prepare for an examination for (JNCIS-ENT/SP/SEC):
- I used Study Guides provided by Juniper Networks Fast Track Program as my main reference.
You may check them here: http://www.juniper.net/us/en/training/fasttrack/
- In my own opinion, those study guides will help you to learn certain topic like OSPF in easy way.
2. I used the old reviewer like the JNCIS Study Guide Sybex Book.
You may also check it here: https://www.juniper.net/us/en/training/certification/JNCIS_studyguide.pdf
- This is quite old but has full of information. It is fore supplement as well.
3. I also watched some videos like CBT Nuggets, WBT.
You may check CBT Nuggets for Junos here: http://www.cbtnuggets.com/it-training-videos/course/jnpr_jn0_1012/8996
4. I read some articles for best practices.
5. Finally, if you have gear; creating your own home lab will help you to familiarized with commands.
I hope this will also help you to improve your prepration for the exam.
Goodluck Kadeken!