First, you should immerse yourself in each major topic when you study it. For example, you might take some time away between studying IKEv1 IPSec VPNs and IKEv2 IPsec VPNS or SSL VPNs, but when studying any of it, take the time to read and practice all the exam material in a concentrated period. The VPN exam has several large topic areas (IKEv1 and IKEv2 IPSec VPNs, Clientless SSL VPNs, AnyConnect VPNs and High Availability) that fit this strategy well. As usual, there is time pressure on achieving a certain level of certification; thus, a wrong approach to your studies will eventually catch up with you as more and more gaps start accumulating due to a rapid but incomplete learning path.
Bear in mind that it is not enough to understand the technology; you also need a good study approach so you can easily remember commonly used topics as well as advanced, cumbersome ones. For this there is no common approach; you need to make your own algorithm to easily make connections between topics and find your own best strategy.
Practice. Buy gear, use emulators, use simulators, rent or borrow gear, but plan to practice the configurations and spend time understanding the show commands. Use as much as possible debug commands to get a better understanding of what goes on during a functional configuration. Break it, use debug commands again, and observe if outputs are friendly enough to give you hints on where the errors lie.
Learn each topic deeply. CCNA and CCNA Security cover a much broader set of topics than does any professional level exam, which goes much deeper into a certain technology area. To learn the topics to the required depth, read your primary study sources, review the material and practice every aspect of it. It is also helpful to use multiple study sources when possible, in order to get a different view or opinion, which might be easier for you to follow and understand. Nevertheless use certified forums and blogs which often times make a good job on explaining how stuff works, and where you can ask experts about your issues.